Computer Systems - Computer Studies Form 1 Notes

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Introduction

  • The term System can be defined as a collection of independent entities that collectively work together to achieve a desired goal.
  • All things can be viewed as being made up of small independent components (subsystems) that come together to form a bigger more complex system.

For example;

  1. A School can be seen as a system with students, teachers, Accounts department, and the Administration as subsystems. The school system itself is a subsystem of the ministry of education.


Computer Systems.

What is a Computer System?

  • The term Computer system refers to the complete set of devices required to use & operate the computer.
  • Computer system is the complete set of devices that make a computer work as one unit.
  • A collection of entities that work together to process and manage information using computers.
  • A computer system consists of the computer itself & supporting devices for input, output, processing & storage of data such as disks, Monitors, Printers, etc


Functional Organization of the Elements of a Computer system.

  • A Computer system consists (or is made up) of 4 basic elements that are interrelated and work in unison. The four elements are:
    1. Hardware.
    2. Software.
    3. Liveware (Computer user).

functional organization of a computer system

Hardware.

  • Hardware is a term used to describe all the physical & tangible devices that make up a computer system, i.e. it consists of the parts that can be touched and felt.
  • Hardware include all mechanical & electronic elements found in the computer, e.g., the System Unit, Transistors, Diodes, bus systems such as electronic paths (channels), the Input devices (e.g., Keyboard, Mouse), Output devices (e.g., Monitor) & the Storage devices.
  • Hardware devices enable the user to enter information into a computer, view the output on screen, print out our work, store and process the work.
  • The hardware elements of a computer are generally grouped/ sub-divided into 4 major categories:-
    1. Input devices.
      - Input devices are used to communicate with a computer. They enable the computer user to enter data, information & programs into the computer. They also let the user issue commands to the computer.
      - An Input device converts the input information into machine-sensible/ readable form.

      Examples.
      • Keyboard.
      • Mouse.
      •  Key-to-disk.
      • Key-to-Tape.
      • Scanner.
      • Light pen.
      • Trackball
      • Video digitizers.
      • Graphics pads (Tablets).
      • Joystick / Game paddles.
      • Speech Recognition devices. * Digital & Web cameras.
      • Voice input devices, e.g. Microphones.
      • Document readers, such as, Magnetic Ink Character Reader (MICR), Optical Mark Reader (OMR) & Optical Character Reader (OCR).
      • Point Of Sale terminals, such as, Bar code readers, Kimball Tag readers, Card readers, & Badge readers.
    2. Central Processing unit CPU (Processor).
      - The CPU is composed of the Main Memory, the ALU & the Control unit.
      - The CPU performs the necessary operations on the data held within the memory. It interprets & processes all the instructions from the Input devices.
      - The CPU is housed in the computer casing (System Unit), which contains all the major components of a computer system.
    3. Output devices.
      - Output devices are used to extract/ disseminate processed data from the computer. They display the results of all the information that has been processed.
      - They also convert machine-coded output results from the Processor into a form that can be understood by people.

      Examples.
      • Screen (Monitor/ Visual Display unit VDU).
      • Printers
      • Audio Response units.
      • Graph Plotters. 
      • Sound output devices, e.g. Speakers. 
      • Microforms.
    4. Storage devices.
      - These are devices used to store data & programs in computers. They include; Hard disks, Floppy disks, Magnetic tape drives, Cassette Tapes, Optical disks (CD-ROMs), and Random Access Memory (RAM).
      - Note. All these storage devices differ in the way (technology) they store data & the capacities of data they can hold.

hardware classification

Characteristics of Computer Hardware.

  1. Hardware consists of parts that one can touch and feel.
  2. Hardware determines what software will be used in the computer.
  3. Computer hardware is expensive to acquire.
  4. Hardware devices can only be made by specialist hardware engineers.
  5. Not easy to change particular hardware components.

Software.

  • These are the programs & data used in a computer system that enable it perform a no. of specific functions.
  • Software is a set of computer programs that guides the computer in each and every activity that happens inside the computer during data processing operations.
  • Software also includes the associated documentation (descriptions of the programs).
  • When used in a computer, Software instructs the computer to carry out specific processing tasks, e.g. produce the year end Balance sheet.

Characteristics of Computer Software.

  1. They are the programs & data used in a computer system.
  2. A Computer Program is usually a set of computer instructions written in any of the computer programming languages, e.g. BASIC, PASCAL, etc.
  3. It is not possible to see a program in memory as it exists in magnetic spots, however, you can see & touch a listing of the program on the computer screen.
  4. Software enable computer hardware to operate effectively. In other words, software is meant to put ‘life’ into the hardware.
  5. Software is flexible, i.e., the software used in a particular computer is relatively easy to change.
  6. Software is cheaper compared to hardware devices.
  7. Computer software can be written by the user, a Programmer or a Software house.

Liveware

  • Liveware is a term used to refer to the computer end-user. They are the people who coordinate the various activities, which are necessary to get a computer system to perform useful tasks.
  • They include; Data entry operators, Computer Operators, Programmers, System Analysts, Data Processing Managers, Database Administrators, Computer Librarians, and the other staff directly or indirectly involved in the running of the system operations.
  • Apart from the hardware and software elements, the user is also seen as an integral part of the computer system as shown in the figure below;

integral parts of a computer system



Electronic Components of a Microcomputer System.

  • A microcomputer consists of 4 electronic parts:
    1. Input devices.
    2. Central Processing Unit (CPU), also called the Processor.
    3. Output devices.
    4. Memory storage devices, which consist of Main memories & Secondary memories.

a computer model

  • Data & instructions to be processed are supplied to the computer memory by the user with the help of Input devices.
  • The CPU performs the desired operations on the data and the results of calculations/ processing are communicated to the user through the Output devices.
  • The data and/or instructions not being used immediately by the computer are held permanently in the Backing storage, for retrieval any time it is required by the user.


Input Devices.

  • Before a computer can process any data, it must be given the data & program instructions by use of an Input device.
  • Input is a term used to describe all that goes into the computer memory (usually the raw data & instructions) to await processing.
  • Input involves entering data & instructions into the computer by use of suitable devices.

Functions of Input Devices.

  • An input device performs the following functions/ tasks:
    1. Accepts data & instructions from the user into the computer system.
    2. Read data from the medium on which it is stored.
    3. Converts the human-readable data into electronic/machine-readable form (i.e. a form that can be understood by the computer)
    4. Accepts commands for running, halting or aborting a program from the user.
    5. Data input can either be Online or Off-line.
  • Once the data is entered into the computer, it finally enters the Main storage.

Classification of Input Devices.

  • Input devices can be classified according to how they are used to enter data into a computer.
  • These include.
    1. Keying devices.
    2. Pointing devices such as the Mouse, Trackball, etc.
    3. Scanning and other data capture devices, e.g., Scanners, Digital cameras, etc.
      - Data capture devices are those devices that automatically capture data from the source.
    4. Speech recognition or Voice input devices such as Microphones.
    5. Touch screen and Digitizers.

Keying Devices.

  • Type of keying devices
    • Traditional keyboard
    • Flexible keyboard
    • Ergonomic keyboard
    • keypad.

Pointing Devices.

  • These are the input devices that enter data or instructions by controlling a pointer on the screen.
    Examples of pointing devices are; Mouse, Trackball, Joystick, and Light pen.

Mouse.

  • A mouse is a pointing device that rolls on a small ball and is used to control the movement of the cursor (or, a pointer) on the computer screen.

    Types of mouse
    • Traditional mouse
    • Optical mouse
    • Cordless mouse
  • The mouse is mostly used with Graphical User Interfaces (GUIs). It issues commands to the computer by activating certain simple graphic images called Icons displayed on the screen.

Advantages of using a Mouse.

  1. The mouse is easy to learn & convenient to use. This is because; it is used to select options (icons) displayed on the screen.
  2. It is inexpensive.
  3. Most modern software includes an option to use it.
  4. It performs operations much easier & much more quickly than a keyboard. It is very fast to work with as it lets the user provide simple “point” & “click” instructions to the computer.
  5. Can be used in art and design work because; it allows diagrams to be drawn & modified easily.

Disadvantages of using a Mouse.

  1. The mouse cannot be used to input text easily.
  2. It is relatively slow for selecting menu options. A user who is familiar with the keyboard commands can select the options more quickly.
  3. It is not very accurate for drawing purposes.
  4. The mouse requires a flat surface to operate.

Trackball.

  • A Trackball works just like the mouse, but instead of moving it on a flat surface, it has a ball fixed on its top which is rolled using the index finger.
  • As the ball rotates, it moves a pointer on the screen. The user can then click its button to execute the selected command.
  • The advantage of a trackball over the mouse is that, a Trackball doesn’t require a flat surface for movement.
    Note. Today some computers come with a trackball on top of a Keyboard and a Mouse.

Light Pen.

  • A Light Pen is a hand-held device similar in shape to a ball-point pen, and has a light sensitive point. It consists of a pen-like device called a stylus connected by a cable to a computer terminal.
  • A Light pen is used together with a graphic VDU that is able to sense light shining on the screen using special hardware & software. A Light pen does not emit light but instead, it reacts to the light emitted by the display using a photosensitive detector at its base.
  • When the pen is moved across the screen, its position is sensed because of the light it produces.
    • A Light pen provides a direct input mode. It can be used to read data directly from the source document. It allows the user to point directly to an object on the screen, thus identifying it to the screen.
    • Light pens can be used to read bar-codes on the different items.
    • It can also be used to select items from a given list of ‘menus’ displayed on the screen by simply pointing the pen at the item required & then pressing a button on the pen.
    • Light pens are usually used as design aids - they can be used to draw images on the screen, which can be printed. They can also be used to indicate a point on a screen or pad, for example, to select options for drawing.

Joysticks/Game Paddles.

  • These are hand-held Input devices, which enable the user to interact with a program. They are used for playing computer games.
  • Joystick is an input device that looks like a car gear lever. It is an analogue-to-digital converter where the input involves moving the control lever sideways, upwards or downwards to control the movement of the cursor on the screen.
  • Just like the mouse, it has a button which is used for selecting an item. It is commonly used in playing video games.
  • Game paddle may consist of a button, which can be pressed by the user to input data to the program. When the program senses that the button has been pressed, it takes the appropriate action, such as, firing a missile or reversing the direction of a tank.
  • A Game paddle can also consist of a dial which when rotated; it conveys information to the program. The program must immediately act on the information supplied by the dial setting, e.g. a goalkeeper may be moved across the face of the goal to intercept a shot.
    Note. Data processing should be very fast.

Touch-sensitive Screens.

  • A Touch-sensitive screen uses the human finger as the input medium, (i.e. one can select items or options from a given list by touching the screen with a finger).
  • This method of input is usually used with a VDU, which is able to sense the touched points on the screen.
  • When the user touches the screen with a finger, it blocks out the light emitted from that portion of the screen. The computer detects the position of the finger. The screen can then determine which part is being touched, and therefore, which selection is required.
  • Touch screens are mostly used in public places like banking halls, hotels, in airports (to provide guidance information), etc.

    Notes.
    • Both the Light pen & the Touch provide fast input modes.
    • There is no typing or printing required; however, they operate under the influence of complex programs.

Digitizers.

  • The Digitizers are input devices that convert graphical drawings or images on the paper or other material into digital data and convey them to the computer memory.
  • Digitizers are slow, but easy to handle and errors are hardly present.

Graphics Pads/Tablets.

  • Graphic Tablets are used for entering drawings directly into the computer.
  • A Graphics tablet consists of a pad or tablet (that is sensitive to touch) & a pointing device, which is similar to a ball-point pen called a stylus.
  • A paper is placed on the graphic pad & the user can trace lines and draw pictures using the pen. As the stylus moves on the tablet, the tablet senses the pressure on it & translates it into digital signals giving its corresponding position on the screen. It then converts this ‘pressure’ into x-y co-ordinates, which describe what is being drawn. This data is then relayed to the computer, which can display the drawings on the screen or have them printed.

Uses of Graphic Tablets.

Graphic tablets are mostly used;

  1. In Engineering & Architectural design as it lets the user create his/her own images. It is very easy for the user to ‘try out’ different designs.
  2. In Computer-Aided Design work as diagrams & maps can be traced or drawn & transferred into the computer memory to be further worked on using Graphics programs.
  3. By Banks & Insurance companies to verify signatures. A signature written on a pad is compared against another formerly stored in the computer.
  4. Pads are also good at detecting forgeries.

 

Video Digitizers

  • These consist of special hardware & software, which converts video signals frame-by-frame into a digital representation in computer memory, which can be saved on disk, if necessary.
  • A sequence of frames can have graphics, cartoons, text added, etc.

Digital Cameras.

  • A Digital camera stores its images in digital form. These images can then be streamed (entered) directly into a computer for editing or printing by connecting the camera to a computer using a special cable.
  • There are 2 types of digital cameras; one that can take still (motionless) images, i.e., photographs, and another that takes motion pictures (video).

Voice Input Devices (Speech Recognition Devices - SRD).

  • Voice recognition is a type of input method where a Microphone connected to a computer system (through some extra circuitry) is used to enter data in form of spoken words into the computer.
  • The SRD accepts spoken commands & convert them into electronic pulses/ signals, which can be processed by the computer.
  • The user must train the system to recognize his/her voice by repeating each word in the vocabulary several times. Each word is analyzed & filed for identification.

Uses of Voice Input devices.

  1. Voice input is a fast & easier method mostly suitable for the handicapped especially those with impaired hands.
  2. In Security & Access control – Each person has a unique ‘Voiceprint’ that can be used for identification. This approach could be used in; -
    • Electronic Money transfer.
    • House/ Car security using voice activated locks.
    •  Office security for room access.
  3. In Voice-activated toys & games.
  4. In Quality control & automation (computerization/mechanization) in factories.
    - A checker whose hands are busy does not have to stop working to make entries in log books, instead he/she can simply give a running (spoken) comments on the goods he/she is examining. For example, in Japan, speech input is used to order robots about.
  5. In Automated materials handling – in airports, handler’s give spoken commands that direct the luggage to the appropriate conveyor belt.
  6. In Computer-Aided Design (CAD) A designer, e.g. of buildings, working at a terminal can call up design patterns which are frequently used, instead of having to punch catalogue nos. into a Keyboard.

Limitations (Disadvantages) of Speech Input/Recognition devices found Today.

  1. Homophones some words have same sounds.
  2. Word separation.
    - The speech must be “clipped” i.e. each word must be followed by a short period of silence.
    - This enables the device to recognize the end of each word. If this is not done, the device might not be able to tell the difference between ‘Command” and “Come and”, depending on the accent of the speaker.
  3. Speaker variability.
    - The speed, tone (quality of sound), accent, loudness and pronunciation of an individual speaker can vary
    - Voice input is complex to develop, and it does not take care of speech related problems such as accents and tone. This implies that the device must learn the unique speech of an individual.
  4. Limited vocabulary understood & the no. of speakers they can recognize.
    - Most speech systems can recognize a limited, standard vocabulary of spoken words. The simplest SRD can recognize the voice of only one speaker. .
    - The device must also be ‘taught’ the voice patterns of the speaker. For example, if a device can store a vocabulary of 25 words, the user will speak the 25 chosen words into the device.
    - The device then stores the patterns for the spoken words. Later, when the user speaks a word, the device compares the pattern of the word spoken with those patterns it had previously stored. If a match is found, the word is recognized. If not, the speaker may be requested to repeat the word or use a synonym (a word that means almost the same thing).
  5. The response rates of these devices are still relatively slow.
    - When you compare the no. of words in English & the total no. of words that can be said at a given point, show that speech recognition is slow.
  6. Speech input is complex to develop & is still at the early stages of development.

Scanning Devices.

  • These are devices that enter (capture) data into the computer directly.

Image scanners.

  • A Scanner is used to input pictures or photographs into the computer. This is because a Keyboard or a Mouse cannot perform these tasks.
  • Scanners are usually used to capture existing documents in an electronic form into the computer for further processing or incorporating into other documents.
  • It converts text & graphics into machine sensible format. Once the text & graphics are scanned, the images can be manipulated by changing the colors, the sharpness and contrast.

    There are 2 main types of Scanners: -
    • Page scanner:
      - This is a desktop machine that looks like a small photocopier. It scans a whole page at a time. An example is the Flatbed scanner.
      - Using this scanner, one can scan text, a real object or a picture by placing it on a glass plate exactly the way a photocopying machine works. The text or the picture scanned is displayed on the screen or saved so that one can edit or print it.
    • Hand scanner:
      - A Hand scanner is held in the hand and passed over a document.
  • Scanners are very useful when large amounts of existing documents need to be converted into electronic form for feeding into a computer system.
    For example, if the contents of the Bible are to be entered into a computer system, you can either type everything using a Word-processor, or scan each of the pages and import them into a wordprocessor, which is faster and also more accurate.
  • Each character is compared to all known shapes or patterns so that the appropriate code can be entered into the computer.

Scanner Problems.

  1. The scanner is on but there is no image when you scan.
    • Make sure the DMA, IRQ and Address jumper settings on the interface board matches the settings you selected in the Scan Mate installation program.
    • Check the brightness control dial on your Scanner. If the dial is at the brightest settings, you may not be able to see the image.
  2. The light on the scanning window cannot turn off.
    • This shows that there is a conflict with resident software on DMA channel.
  3. The images printed look blotchy (discoloured/ spotted).
    • To prevent this, do not rescale the image. If you scale the image, you will lose some of the details when you print. If the image is too big, scan at lower resolution.
  4. The Scanner turns off as soon as you start scanning.
    • This shows there might not be enough RAM to scan the images.
  5. The scanned image on the screen is much larger than the original.
    • This occurs if your image is displayed at a lower resolution than you scanned.
      Note. The Size of your screen image depends on your Monitor’s size & your VGA card.

Other Digital Devices

Document Readers.

  • A Document reader is an input device, which can read data directly from source documents, such as bank cheques, & convey it to the computer in form of electronic signals.
  • Types of codes on documents that can be recognized by a Document reader: -
    1. Marks short lines made by hand, usually in pencil on a document.
    2. Characters hand-written (e.g. on meter-reading) or printed in magnetic ink on cheques.
    3. Printed lines e.g. the bar codes.
  • Document readers can be classified into; Optical readers and Magnetic Readers.

Optical Readers.

  • Optical readers use the principles of light to sense the document contents or to capture data. A special type of concentrated beam of light is passed over the object, image or text which needs to be entered into the computer. The reader converts the data into digital form, and then passes it to the computer for processing.
  • There are 2 types of Optical readers: Optical Character Reader (OCR) & Optical Mark Reader (OMR).

Magnetic Readers.

  • They use the principles of magnetism to sense the document characters that have been written using magnetized ink.
    Example; Magnetic Ink Character Reader (MICR).

Optical Character Reader (OCR).

  • Optical Character Recognition (OCR) is a data capture technique, which enables the computer to read printed or hand-written documents directly.
  • The characters are formed onto the document by a Typewriter or computer Printer using a special type font. Handwriting can also be recognized if the characters have been carefully/well formed.
  • The reading is done by OCR, which can be connected directly to the computer. An OCR is able to distinguish one character from another by its shape.
  • As the OCR reads/ scans the document, each character reflects different amounts of light, which is sensed by the OCR using a photoelectric device & converts the shape sensed into electronic signals. These signals represent a particular pattern.
    Note. The Reader has a memory that stores reference patterns for a given character set or font.
  • The sensed pattern is then compared with the stored patterns of the characters, which the reader can recognize. If a match is found, the character sensed is identified; otherwise, the document may be rejected by the reader.

Uses of Optical Character Recognition devices.

  • OCR devices are used by companies that do a large amount of processing on a regular basis. For example, Public utility companies, Insurance companies, Airlines, Banks & the Postal service (for reading postal codes).
    • Public utilities OCR is used to process documents produced as output and which can be reused as input by the computer. For example, an Electricity bill has a returnable slip, which is printed with all the information required for re-input into a computer, i.e., customer code and amount owing. If the customer pays the exact amount stated, the returned portion of the bill is used for direct input to the computer.
    • Used in Sales Order forms.
      - The forms can be printed by the computer with standard data, e.g. Stock codes, Account code, etc. The Salesman then enters details of the order form and returns it for OCR processing.
    • Used in Stock-taking sheets.
      - The computer can print out stock sheets in OCR characters. The stock checker then enters the actual stock quantities on the form in careful handwriting. The sheet can then be optically read into the computer for amending the stock records.

Disadvantages of OCR.

  1. The document should be handled carefully (e.g. it should not be folded or creased) for accurate reading.
  2. Document size & type area may be limited for accurate reading.
  3. It requires special typing & character formation and a paper with the required quality.
    - The user must make sure that characters are well-formed; if they are not, reading errors may arise, making output results unreliable.

Optical Mark Reader (OMR).

  • The documents are pre-printed with predefined data positions. These positions can then be marked by, let say, a pencil.
  • The OMR detects the presence or absence of a mark on a form by sensing the reflected light of these positional marks. The reader is then used to convert the marks into computer-readable data & send the value of the sensed data into the computer in form of electronic signals.
  • The accuracy of an OMR depends on the marks being made properly. If a mark is too light or not solid enough, it may be misread, giving rise to errors.

Uses of OMR.

  • OMR forms are used in situations where the data to be input is simple, or the volume of data is large enough since using other methods would be more expensive.
    • Used in marking Multiple-choice examination papers where the answers are filled in a form with special pencils.
      - The OMR can sense the presence of a pen or pencil mark. The person taking the test makes a pencil mark in the box, which he/she thinks corresponds to the answer. An ‘OMR’ is then used to ‘read’ the answers given by sensing the marks made. This data is then relayed to the computer, which can then check the answers given and grade the paper.
    • In Insurance premium collection.
    • To read marked research questionnaires.
    • In Supermarkets for stock recording.
    • Traffic surveys.

Comparative advantages of OMR vs OCR.

  1. Speeds up data input. They ensure faster & more accurate processing of data.
    - They read data directly from the source document & enable data to be given directly to the computer for processing.
    - With an OCR it is possible to read up to 10,000 A4 sized documents in 1hr.
  2. They read data directly from the source document & therefore, no data preparation is required.
  3. Errors are easily corrected.
  4. The documents can be re-used, thus saving on stationery.
  5. The contents of the documents are both human & machine sensible, hence reliable.
  6. The sensitivity of an OMR can be altered to allow for different surface, pencils and inks.
  7. OMR has a better recognition rate than OCR.
  8. With an OCR, no typing or transcription/recording process is involved & therefore, not prone to transcription errors.

Comparative disadvantages of OMR and OCR.

  1. They are expensive methods of input, because they require specialized techniques & equipment.
  2. Verification of marked data is difficult.
  3. Documents may be difficult to design, understand and fill in.
  4. The document reader will have to be reprogrammed for each new document design.

Magnetic Ink Character Reader (MICR).

  • Magnetic Ink Character Recognition (MICR) is the machine recognition of characters printed with Magnetic Ink.
  • The document characters are typed or printed in ink containing Iron (II) Oxide that gives them a magnetic property.
  • After forming the characters onto the document, the inked characters are magnetized by passing the document under a strong magnetic field.
  • During the reading process, the magnetized characters cause current to flow through the read head depending on the magnetized surface area occupied by individual characters.
  • The reader differentiates characters depending on the magnetic patterns that bring different amount of currents. The MICR recognizes these patterns & conveys them into the computer in form of electrical signals.

Uses/Applications of MICR.

  • Magnetic Ink Character Recognition (MICR) is used in banks to process the many cheques being written each day.
    - The MICR mostly uses a font known as E13B, which consists of 14 characters (i.e. digits 0-9, & four special characters).
    - A cheque is usually pre-printed with the Identification number of the bank, the Account number of the customer, Serial number of the cheque, Branch number, using a special ink containing particles of Iron Oxide (Magnetic Ink). When the cheque is presented for payment, the amount is written on the cheque in magnetic ink, using a special device. The cheque can then be read by a MICR. The data read is then transmitted directly to the CPU for immediate processing, or can be stored on magnetic disk for latter processing.
  • In Local Authorities for payment of rates by installment.

Advantages of MICR over OCR.

  1. An MICR can read data faster & accurate since the information on the document is usually pre-printed.
  2. Difficult to forge.
  3. Document can still be read when folded, written on, etc. This means that, MICR is more ‘robust’.
  4. A wider range of fonts can be used, including hand printing & normal type. However, there is no standard-type font.
  5. Faster than OCR. It is possible to read about 2,400 A4 sized documents 1 minute.

Point-of-sale (pos) Terminals.

  • This is a general class of Input devices of which a Bar-code reader is an example.
  • A POS terminal can be used as an Input device when online processing is required. Data arising out of a transaction (e.g. the purchase of an item) is entered on the terminal and is immediately processed by the computer.
  • POS terminals are widely used in the Banks & computerized Wholesale or retail industries, such as Supermarkets.
  • Each item in the store has a code; Universal Product Code (UPC) printed on it, that identifies the item.
  • The POS terminal consists of a Numeric keypad & a few Control (Functional) keys for entering data, a Screen and a Printer to print out the list of items and price for the customer.
  • The Item code, Quantity & Price of the goods purchased by the customer is entered into the POS terminal directly by the operator. The terminal produces the customer receipt. The details of the sales are then entered directly into a backing storage device and the Stock level is also automatically decreased.
  • A Bar code reader, a Credit card or a Kimball tag Reader could be attached to a POS terminal to reduce the data entry.

Bar-code Reader.

  • This is a device used to read the bar-codes printed on many items in Supermarkets Pharmacies.
  • Each item is given a code known as Bar-code (a Bar-code is a set of parallel bars of varying thickness & spaces of varying widths representing a number code). A space represents a “0” while a bar represents a “1”. The coded data can be read by using the principles of light.
  • A computer is used to store the code of the items, item description, price, amount in stock, etc.
  • When a Bar-code reader is moved across the bars by the Cashier, the reader scans the bar codes printed on the item using a laser beam, which generates electrical pulses corresponding to the reflected light received. The bar code is then converted to a number (which is the code for the item).
  • The interpreted data is sent to the computer memory in form of signals. These pulses are compared with standard codes stored in the computer and is used to look up the price of the item. The details of the price & description are printed out on a receipt for the customer. The Store Inventory may also be updated at the same time.
  • Bar codes are also used in Library lending Systems. Each user is given a library card, which is coded with his library User Number. The relevant details of the user; let say, Name, AddressTelephone number, category of user (e.g., Staff or Student), No. of books borrowed, date of expiry of the card, etc are stored in a file on a disk.
  • When the user wishes to borrow a book, a Bar-code reader ‘reads’ his card, and transmits the code to the computer. The computer uses the code to retrieve the user’s record from disk.
  • The Library Assistant will then update the user’s record by entering the relevant information such as the name (or number) of the book, the date borrowed & the date on which it is to be returned.
    Note. Bar-codes cannot be used on goods such as Fresh Fruits & Vegetables.

Advantages of using a Bar-code reader.

  1. They are very fast & accurate provided that the bar-code has been printed clearly. For example, if the bar-code is soiled by dirty hands or has broken bars, errors may occur when an attempt is made to read the code.
  2. It is a cost-saving method.
  3. Saves time. The prices do not have to be attached to each item in the store because the items details are already held in a master file.
  4. Does not require special skills to operate.
  5. It improves customer convenience.

Disadvantages of using a Bar-code reader.

  1. Requires standby facilities.
  2. Requires very expensive equipments.
  3. The prices are not stamped on the product, and therefore, high chances of incorrect data being entered.

Kimball (Punched) Tags.

  • Some manufacturers use Kimball tags; small paper punched cards attached to clothes or other commodities on sale mostly in supermarkets. The data is incorporated in the small punched holes. The holes alternate with spaces to represent data in binary digits.
  • An optical scanning method is used to read the Kimball tag and extract the product code & price from it. The tags are removed at point of sale and transferred to the data processing department for their contents to be used in updating the stock files.
    Note. POS terminals, Bar-code readers & Kimball tags speed up customer service & also ensure accuracy. They may also be used to manage inventory, accounts & maintain up-to-date sales information.

Advantages.

  1. Data is already coded, hence easy to process.
  2. No transcription requirements.

Disadvantages.

  1. Difficult to handle because they are small.
  2. Store small volume of data.

Cards/Badges.

  • These are small rectangular cards made of plastic that incorporate data in both machine-sensible & human-sensible forms, e.g. Credit cards.

    Ways of Coding data onto badges: -
    • Magnetized marks, e.g. a short strip of magnetic tape sealed into the card’s surface.
    • Optical marks.
    • Punched holes.
  • The cards are read using Badge readers. The data recorder machine records data on these badges automatically, once manually inserted, using magnetized marks, optical marks or punched holes.
  • For reading, the badge is slotted into the reading unit where the converter machine (the reader) accepts the contents of the badge and conveys them directly to the computer as input for processing.
  • The badges are used in banks as Credit and Service cards, e.g., in the Automated Teller Machine.
  • The Badge contents are usually static, though some cards contents can be altered by the reader, e.g., Phone credit cards whose currency value keeps on changing until zero currency value is left.

(a). Smart Cards.

  • A Smart card is a special type of badge whose data can be changed by a special badge reader.
  • A Smart card can be used as a form of electronic money. As the customer purchases an item, the badge reader can deduct units from the card. This process continues until the card has no more currency units left.

(b). Credit Cards.

  • A Credit card has a strip of magnetic tape fixed on it. The tape contains coded information, which is usually the owner’s code. The card is inserted into a slot where magnetic data may be picked. Details of the transaction are then recorded against the credit card no. & the owner’s account is credited with the transaction.

Uses of Cards/Badges.

  • In Car parks badges are used to raise car barriers, allowing entry to or exit from a car park.
  • In Banks Credit and Service cards, i.e. Automated Teller Machines (ATMs) give out cash automatically when customer inserts a plastic card & follows the instructions issued.
  • In Access control Access control cards are used in many offices to control access to buildings or rooms for security reasons.
  • In Production control Punched cards can be used to hold data in a factory such as employee’s details, etc, which is used for production scheduling (arrangement), stock control and job costing.

Direct Input From Instruments.

  • Sensors are devices that can be connected to computers & are used to record physical quantities like Temperature, light, humidity.
    Examples of direct input instruments: -
    1. Sensors used to record temperature, light, humidity in a Green house to ensure the best conditions for plant growth.
    2. Thermostats connected to a Central heating system controlled by a computer in order to monitor temperature & to help save electricity.
    3. Pressure pads on a road connected to computer-controlled traffic lights to speed traffic flow.
    4. The continuous logging of temperature data in order to monitor & subsequently control a chemical process. The automatic capture of data for use in such processes is usually known as Data logging.

Advantages of using devices, which can read data directly from source documents.

  1. They ensure faster & accurate processing of data. This is because the data is read directly from the source document, and no data preparation is necessary.
  2. No typing or recording required, and therefore, not prone to transcription errors.
  3. The documents can be re-used, thus saving on stationery.
  4. The contents of the documents are both human & machine sensible, hence reliable.
  5. Errors are easily corrected.
  6. Difficult to forge.


Central Processing Unit(CPU)/Processor.

  • The CPU is described as the computer’s ‘brain’ that monitors all the computer operations. It is the unit inside the computer where all software instructions, math and logic operations are carried out.
  • In Microcomputers, the CPU is implemented in a single silicon device called a Microprocessor (Computer chip), which is made by combining a very large no. of transistors together using a technology referred to as Very Large Scale Integration (VLSI).

Notes.

  • The CPU is one of the most expensive components of the Motherboard & also a very delicate piece of equipment.
  • The CPU has a label, such as “486” or “Pentium” to show its type, and the chip manufacturer’s logo on it.
  • It has a large fan (known as the Heat sink) screwed on top of it, that keeps the CPU cool while the system is on. This is because the CPU gets very hot when it is in operation.

Functions of the Processor (Central processing unit).

  1. To control the use of the Main memory in storing of data & instructions.
  2. To control the sequence of operations within the computer.
  3. To give commands to all parts of the system.
  4. To carry out data processing.

Basic Features (Functional Elements) of a Microprocessor system.

- The Processor is made up of 3 major/ main components

  1. Control Unit (CU).
  2. Arithmetic Logic Unit (ALU).
  3. Main Memory Unit (MMU).

- Other components include;

  • Registers.
  • Accumulator.
  • Buses.

- Note. The elements making up the Computer system communicate through electronic paths called Buses. The buses carry data, instructions, information, control commands and power between the communicating elements.

Control Unit (CU).

  • The CU acts as the manager of the computer. Its main work is to control, supervise & coordinate all the activities of the various units of the computer, enabling the machine to perform useful tasks.
  • The CU is usually described as the Nerve centre of a computer system. It co-ordinates & controls the activities of the different components of the computer system in the same way that the brain directs the actions of the body.
  • The CU carries out the fetching, decoding & execution of the instructions. It fetches/ selects the required instruction from Main storage, stores it in a no. of special Registers, interprets the instructions, and causes the instruction to be executed by sending appropriate signals to the appropriate hardware devices.
  • In order to execute an instruction, the CU must do the following:
    • Fetch (get) the instruction from the Memory.
    • Decode the instruction, i.e., determine what the instruction is saying. For example, whether to ADD or COMPARE two numbers.
    • Get the data required by the instruction. E.g., the two numbers.
    • Activate the right circuits for the instruction to be obeyed, e.g. call into action the circuits which perform addition.
  • Note. The CU automatically repeats this cycle of operations until either it is instructed to stop or the last instruction has been executed.
  • In order to enable the Control Unit to carry out the various functions, certain registers are used.
    1. Sequence Control register (also known as the Program Counter).
      - It controls the order in which the instructions are carried out.
      - It contains the address of the next instruction in the computer program to be executed.
      - For the next instruction to be executed, it must be brought from the memory into the Processor. When an instruction has been fetched from memory, the Program Counter is increased by 1, and is then ready to find the next instruction.
      - Therefore, the Sequence Control register sequentially points to the address of the instruction to be carried out, reads it into the Instruction Register, and automatically moves to the next instruction in the processing sequence.
    2. Instruction Register.
      - It stores a copy of the instruction being processed.
      - Note. An instruction has 2 parts;
      • Operation part, e.g., Multiplication.
      • Address part.

      - The Instruction Register is connected to the Instruction Decoder.
    3. Instruction Decoder.
      - It decodes (interprets) the instruction received from the Instruction Register & sends signals to the control switches of the computer.
    4. Address Registers.
      - Each location in a memory has its own address, which allows us to get directly to any program instruction or item of data stored within the memory.
      - Address A label, name or a number identifying a storage location, or a device from which information is received or to which it is transmitted.
      - Address Registers are 16-bit registers used for the storage of addresses. They are connected to the Address Bus.
      - The Address part of the instruction goes to the Address Register, which retrieves the required data item in the address indicated and copies it in the ALU so that the operation instruction may be executed.
      - Address modification the process of changing the address part of a machine instruction by means of coded instructions.
    5. System Clock.
      - In order to be able to fetch & execute instructions, the CU uses a timing signal provided by a System Clock attached to the CPU. The Clock is an electronic system that is used to control the Processor on when to fetch the next instruction from the Main memory.
      - The Clock sorts out all the internal paths inside the Processor to make sure that data gets from the right place & goes to the right place.
      - The clock is an Oscillator that generates timing pulses (at a frequency of several Megahertz) to synchronize the computer’s operations & ensure that the operation occurs at the right time.
      - The CU performs 1 step of the instruction in 1 clock pulse. The speed of processing will depend on:
      1. CPU Frequency, i.e., time duration of 1 clock pulse.
      2. The no. of steps involved in executing a full instruction.
      3. The Access time of the computer, i.e., the time required to access any one memory address.

Functions of the Control unit.

  1. It co-ordinates & controls various parts of the computer system, namely; Main memory, ALU & the Peripheral devices.
  2. It maintains order & controls all the operations or activities inside the Processor.
    - The CU controls the activities of all the other units of the computer by using the appropriate control signals. For example, it instructs the ALU on which arithmetic or logical operations are to be performed.
  3. It connects the required circuits to enable the ALU to process the data in storage, as specified by the program.
  4. It directs sequence of operations, i.e., it generates synchronization signals & manages commands exchanged between the ALU, I/O units & the Memory.
  5. It retrieves and interprets instructions from the Main storage & makes the computer to execute these instructions by giving commands to the rest of the computer elements.
  6. It controls the transfer of unprocessed data to the Main storage & results from the Main storage.
  7. It stores the results in the memory.
  8. It determines the location of the memory that contains the next instruction to be retrieved.
  9. It monitors the CPU operations & identifies problems, such as equipment malfunction, illogical instructions or erroneous data finding its way into the system, and flashes them on the computer screen.

Arithmetic Logic Unit (ALU).

  • This is the part of the Processor that performs all the arithmetic operations, such as adding or multiplying figures, & logical operations needed to solve a particular problem.
    For example, if two numbers are to be added or multiplied, this is done by the ALU.
  • The ALU also performs Logic Functions, e.g., AND, NOT, OR, TRUE, FALSE & IF.

Functions of the ALU.

- The ALU has 2 main functions:

  1. It carries out the Arithmetic operations.
  2. It performs logical operations and comparison on data.

- Other minor functions include;

  1. It performs output of variable (logical) functions.
  2. It performs branching of prefixed conditions.

Accumulator.

  • It is a storage device in the A.L.U, where all the answers from both arithmetic & logical operations are stored temporarily before being transferred to the memory.
  • A Register in the ALU in which operands are placed, and in which arithmetical results are formed.

Computer Bus.

  • A computer bus consists of a set of parallel wires connecting the Processor to the other devices of the computer.
  • It is a communication path/medium within the computer that allows different elements of the computer to communicate with each other.
  • An electrical connection linking internal sections of a computer, such as Processor, Expansion cards, and peripherals such as Keyboard and other Input devices.
  • A parallel collection of conductors that carry data and control signals from one unit to another.

computer bus

There are 3 major types of computer buses:

  1. Data Bus.
    - It is a bi-directional (2-way) bus that carries information & data to and from the Processor, i.e., it carries data from the Processor to the memory during Write operations & from memory to the Processor during Read operations.
    - The Data bus usually carries data for processing.
    - It consists of 4, 8 or 16 lines each carrying 1 bit at a time.
    Note. The Data Bus determines the Bus Width of the microprocessor. Its size indicates the moving capability of information of the chip.
  2. Address Bus.
    - It is a unidirectional (1-way) bus from the Processor to the external devices. It usually contains the address of the memory location or device to be acted on by the Processor (i.e. it conveys addresses).
    - The Address bus is wide (usually between 4 32 lines) to enable it to address as many devices as possible.
    - The size of the Address Bus tells you how much memory the chip can handle.
  3. Control Bus.
    - It’s a unidirectional (1-way) bus that carries command (i.e. timing & control) signals from the Processor. These signals are necessary to coordinate the activities of the entire system.
    For example, the command for the Printer to prepare to receive data is a control signal from the processor.
    - They usually have 3 10 lines.
    Note. Buses are implemented as actual communication lines. They may be Internal buseswhich are usually laid down as a circuit on the chip itself, or they may be External busesimplemented as cables.

Classification of Microprocessors.

- There are 2 basic factors (parameters/ considerations) used to classify Microprocessors.

  1. Clock speed.
  2. Width of the Data Bus.

 

Clock Speed.

  • Every Microprocessor has a clock that drives its operation. Clock speed is the speed at which the processor runs.
  • Microprocessor speed refers to its Clock speed, which is measured in Megahertz (MHz million cycles per second).
  • The Clock speed varies from one processor to another. Microprocessors with faster clocks perform operations much faster compared to those with slower clocks. Therefore, the speed of a microprocessor gives its power the higher the speed, the more powerful the microprocessor.
    Note. The speed at which a computer can process data is also affected by the speed at which the memory can work.

Bus Width.

  • The size of the Data Bus determines the Bus Width of a microprocessor. It indicates the moving capability of information of the chip.
  • Higher Bus widths provide higher computer performance. For example, fetching a 16-bit instruction from memory using a Data bus width of 16 bits would require a single fetch operation, whereas an 8-bit Data bus would require 2 cycles to fetch the same instruction; hence slowing the execution of the instruction.

Types of Processors.

  1. Microprocessors.
  2. RISC (Reduced Instruction Set Computer) processors.
  3. CISC (Complete Instruction Set Computer) processors.

Microprocessors.

  • The Microcomputers use Microprocessors, which usually have all the required functions on one chip.
  • Some of the manufacturers who make microprocessor chips include;
    • Intel Inc., AMD (American Device Manufacturers) & Cyrix who manufacture microprocessors for IBM compatible microcomputers.
    • Motorolla for Apple computers.

Microprocessor Trends.

  • The following are some of the Microprocessors manufactured by Intel Inc:
 Processor  Year  Speed (MHz)  No. of Transistors  Data Bus width(Bits)  Size of Internal Registers(Bits)  Maximum addressabke Memory  No. of Memory Address Lines
 8088  1979  5-8  _  8  16  1 MB  20
 80286  1982  10  130,000  16  16  16 MB  24
 80386  1985  12-16  275,000  32  32  4 GB  32
 80486  1989  33-66  1 Million  32  32  4 GB  32
 Pentium 75  1993  90-200  3 Million  64  32  4 GB  32
 Pentium Pro  1995  180-200  5,500,000  64  32  64 GB  36
 Pentium MMX  1997  166-233  7,500,000  64  32  64 GB  36
 Pentium II Xeon  1998  233-300  7,500,000  64  32  64 GB  36
 Pentium III  1999  500-550  7,500,000  64  32  64 GB  36
  • Pentium MMX has Multimedia instructions such as 3-D bitmap manipulation built in them. The
  • Pentium III Multimedia instructions are 4 times more powerful than those of Pentium MMX Microprocessors.

Advanced CPU’s.

  • Larger computers such as Supercomputers, Mainframes & Minicomputers use Processors made of separate, high speed sophisticated components. That is, the CPU components in large computers are not all on one chip.

RISC Processors.

  • The RISC processors are used in manufacture of Minicomputers.
  • RISC machines are much faster than Micro-processor based machines, i.e. in RISC machines, the time required to execute an operation is much shorter compared to the time a Micro-processor would take to execute the same operation.
  • RISC chips generally use 128 or fewer instructions to execute their tasks. This means that, the processor has few instructions to locate. They can execute these instructions more quickly & are therefore very fast.
  • Again, each instruction is exactly 32 bits long. So, the processor does not waste any power determining where the instructions begin or end. This makes RISC processors more superior.
  • They are also cheaper to produce.
  • Most of the 64-bit RISC machines are manufactured by: -
    • Digital Equipment Corporation (DEC).
    • Sun Microsystems.
    • Hewlett-Packard, and
    • IBM (International Business Machine Corporation).

CISC Processors.

  • CISC chips use between 200 300 instructions. Therefore, the processor has more instructions to look up.
  • The instructions are usually between 8 -120 bits long. This means that, a CPU devotes at least part of its circuit time determining where instructions begin and end, making them run slowly.

Factors that affect the performance of a Processor.

  • Overheating.
  • Incorrect configuration (construction / arrangement).
  • Failed components.
  • Running the processor at the wrong speed.
  • Jammed or clogged or too small heat-sink / cooling fan.
  • Incompatibility.
  • Processor inserted the wrong way.

Measuring The Memory Size of a Computer.

  • The size of a computer’s memory is the no. of ‘units of storage’ it contains. The unit of storage can be a Bit, a Byte, or a Word.
  • A Bit is the smallest unit of storage & can be used to store a 0 or a 1.
  • A Byte is the amount of storage needed/ required to store 1 character.
  • A Character is any letter, digit or symbol, which can be obtained by pressing a key on the Keyboard.
    Note. 1 Byte can be used to store 1 character.
  • A Word is a collection of bits. It can also be described as a group of bits or characters considered as an entity and capable of being stored in one storage location.
  • The no. of bits in a word is called the Word Size. The most common Word sizes are 16, 32 & 64.
  • On a given computer, a Word is the amount of storage normally needed to store an instruction.

Memory sizes.

                                                                                                 Characters
1 Byte                      A group of 8 bits                                          1
1 Kilobyte (KB)         1,000 (a thousand) bytes                10
3         1,024
1 Megabyte (MB)      1,000,000 (a million) bytes              10
       1,048,576
1 Gigabyte (GB)       1,000,000,000 (a billion) bytes         10
       1,073, 741,824
1 Terabyte (Tera)      1,000,000,000,000 (a trillion) bytes 10
12        1,099,511,627,776

  • A computer memory is made up of many storage cells called Bytes. Each cell (byte) is capable of storing 8 bits (binary digits) and has a unique numeric address.
  • Generally, the memory size of a computer is usually measured in Bytes. The prefix K is taken to be 1,024 bytes.
    For example, when the size of a computer memory is quoted as being, say, 256 Kbytes, this implies that, there are 262,144 memory cells or the computer has (256 x 1,024) = 262,144 bytes of memory.

Classification of Computer Memory.

- Computer storage is divided into 2:

  1. Main memory (Primary memory).
  2. Secondary storage (Backing/ Auxiliary storage).

Main Memory.

  • It can also be described as the Primary storage, Internal Memory, Immediate Access storageSemi-conductor memories, Core memory, etc.
  • This is the storage (memory) found within the computer itself.
  • It is used to hold data, programs & instructions required immediately (or currently being used) by the Processor.
  • A computer can only obey data and program instructions that are stored in the Main memory.
  • It is Online (very close) to the central Processor, and therefore, any data within the Main memory is directly accessible to the Processor.
  • The Primary storage generally consists of the following functional areas:
    1. Program storage area.
      - Holds instructions from both System software & Application programs, which enter the central processor from an Input device.
    2. Working storage area.
      - Is used to hold the data being processed as well as the intermediate results of such processing.
    3. Input storage area.
      - It temporarily holds data that has been read from an Input device. Since Input devices operate at slower speed than the Processor, part of the Input storage area serves as a
      - Buffer. A Buffer helps free the CPU to get on with other work while the slower I/O operations are completing.
    4. Output storage area.
      - Holds the finished results of processing unit released to the user. 

General features/ characteristics of the Main memory.

  1. Its operation is wholly electronic, and therefore, very fast, accurate and reliable.
  2. Data must be transferred to the Main storage before it can be acted on by the Processor.
  3. It provides direct data access, i.e., data is instantly accessible from the Main memory & the Processor can act directly on the data.
  4. It is of low/ limited storage capacity.
    - The Internal memory of the computer is designed in such a way that it reaches a capacity beyond which it cannot extend.
  5. It is volatile.
    - For example, the RAM (the section of the Main memory that stores the user programs, application data, instructions and intermediate results during processing) loses its contents immediately when the power is switched off.
    - The Main memory is therefore, used to store temporary programs and data.
  6. The speed of the processor depends on the Main memory.
  7. It is very expensive, due to the technology involved & the elements used in making them.

Question. Identify the advantages and disadvantages of Primary storage.

Functions of the Main memory.

  1. It stores data awaiting processing.
  2. It stores instructions waiting to be obeyed.
  3. It holds the program instructions & the data currently being processed.
  4. It stores intermediate results of processing awaiting transfer to the output devices, i.e. it stores data awaiting output.
  5. The size of the Main memory affects the speed, power & capability of the computer.
  6. All inputs & outputs are transmitted through the Main memory.

- Ideally, the Main memory is used to store all data requiring processing in order to achieve maximum processing speed.

Classification of Primary Memory.

- The Main memory can be classified into 3 different sections:

  1. The fast Microprocessor Internal Registers.
  2. Read-only memory (ROM).
  3. Random Access memory (RAM).

Read-only Memory (ROM).

  • This is a memory that can only be read, but cannot be written to, i.e., the user can only read the information in it.
  • ROM provides permanent storage of data, i.e., the contents in ROM cannot be changed at will.
  • This is because the program instructions and the associated data stored in the ROM are developed & installed during the manufacture of the computer hardware by the computer manufacturers & therefore, they cannot be changed during normal computer operations; thus the term “Read only”.
  • ROM is a Non-volatile memory - its contents are retained (remain intact) when power is switched off. Therefore, it cannot be affected by switching the computer on & off.
  • ROM forms a small proportion of main storage it contributes to about 30% of Internal memory.
  • ROMs are used in situations where the data or instructions must be stored/ held permanently. It is used to store vital data & programs, which need to be held in the Main memory all the time.
    For example, they are used to store essential files especially those the computer uses while booting (starting) up.

Common uses of ROMs.

The main functions of the ROM are:

  1. It stores Firmware (bootstrap programs) i.e., the essential files the computer uses while booting (starting) up.
  2. It stores the system data & instructions that are necessary for the normal functioning of the computer system hardware.
    For example, it stores the Operating system program, which is necessary for the initial coordination of the hardware & the other OS programs.
  3. It stores Control programs, used for the operation of the computer & peripheral devices.
    For example, the BIOS is stored on ROM because the user cannot disrupt the information.
  4. It stores Translation programs (Code converters), used for converting a user’s program into Machine language.
    E.g., TURBO PASCAL, which translates Pascal programs written by users.
  5. It stores Special functions (facilities) peculiar to a given machine.
  6. It stores Character generators for Printers and Video displays.
  7. It stores ROM Lookup tables.

Types of ROM memories.

  1. Masked ROM.
  2. PROM (Programmable Read only memory).
  3. EPROM (Erasable Programmable Read only memory)

Masked ROM.

  • This is a ROM that can only be produced by the manufacturer.
  • The bit patterns corresponding to the desired contents of this memory must be supplied by the user in a standard format. .

Programmable ROM (PROM).

  • This is a ROM that can be programmed or “customized” directly by the user using a special PROM programmer to suit the needs of a particular task.
  • Customizing is the process by which a standard product is adapted for use in a particular situation.

Erasable Programmable ROM (EPROM).

  • This is a ROM that can be reprogrammed a no. of times.
  • There are 2 main types of EPROMS:-
    1. The UV-Erasable Programmable ROM.
    2. Electrically Erasable Programmable ROM (EEPROM).
      - It is also called Flash BIOS. This ROM can be rewritten through the use of a special software program, that uses electrical pulses.
      Note. This is the way Flash BIOS operate, allowing users to upgrade their BIOS.

Random Access Memory (RAM).

  • It is a type of main memory, which is used by the computer to store data & programs temporarily during the times when they are needed in the Main memory.
  • The term “Random Accessmeans that, data in any area of the RAM can be reached or accessed in the same amount of time.
  • RAM provides “Read and write” facilities, i.e., it allow instructions to be written & read out, and also to be changed at will. Therefore, the computer user/ programmer can control or manipulate the data stored in RAM.
    For example, it is this memory that is accessed during installation of programs; deleting, moving & copying of files.
  • Read refers to the retrieving (recovering) of information from memory, while Write refers to the storing of information in memory.
  • RAM is a Volatile memory, i.e. the contents of RAM are usually lost (rubbed off) when the power supply or the computer is switched off.
  • RAM forms the major proportion of Main storage it contributes about 70% of the Internal memory. It is the memory used in large quantities in Main memory, and every computer must specify its size.

Uses of RAM.

-The functions of the RAM are:

  1. It stores data & instructions awaiting processing.
  2. It also stores the instructions which are being obeyed or whose parts have been obeyed by the computer.
  3. Stores the intermediate results - the results of computer working/ calculations, before they are communicated to the users through the Output units.
    Note. The RAM are usually stores Application programs (computer user developed instructions for solving specific tasks), such as Word processing or Spreadsheets.
    - It also stores user data, to be manipulated by the computer using the user input Application programs. Therefore, the RAM of the Internal memory serves the user.

Types of RAM.

  1. Static RAM (SRAM).
    - A Static RAM is able to maintain its data as long as power is provided to the memory chips.
    - It does not need to be re-written periodically. In fact, the only time the data on the memory is refreshed or charged is when an actual “Write” command is executed.
    - SRAM is very fast & is currently being used in the Main Processor as a small amount of high-speed memory called the Cache memory.
  2. Dynamic RAM (DRAM).
    - A Dynamic RAM uses capacitors to store information. The information is stored in the Capacitors as a charge.
    - Like any charge, the electrical charges in individual memory capacitors of a DRAM will drive away (leak) causing the data to either be lost or changed within a few milliseconds.
    - This means that, unlike SRAM, a DRAM must undergo the Refreshing process, i.e., it must be re-written continually in order for it to maintain its data. This is done by placing the memory on a Refresh circuit that re-writes the data several hundred times per second.
    - Refreshing involves reading the information out of, and then writing it back into the memory, thus restoring a full charge.
    - DRAM is used widely for most computer memories because it is cheap & small.

Advantages of Static RAM over Dynamic RAM

  1. SRAM is much faster than DRAM & it able to keep pace with the Main Processor.
  2. It doesn’t require refresh cycles like DRAM – can retain its data forever.

Disadvantages of Static RAMs.

  1. They are of low data density, i.e. it stores less data bits.
  2. SRAM chips are physically large & much more expensive than DRAM chips.

Advantages of Dynamic RAM over Static RAM

  1. DRAM has a much higher packing density than SRAM, i.e., a DRAM chip is able to store more information than a SRAM chip of the same size.
  2. DRAM chips are small in size.
  3. A DRAM can store a lot of information in a very small space, and therefore cheaper (less expensive) that SRAM. This is the main reason why DRAM is the memory used mostly (or in large quantities) as the Main memory in Microcomputers.

Disadvantages of a Dynamic RAM.

  1. It is much slower than SRAM & is not able to keep pace with the Main Processor.
  2. It requires refreshing in order to retain the information in its memory cells.
    - The charge stored in the capacitor of a DRAM leaks & most of the charge cannot be retained for long or may be lost within a few milliseconds. To preserve the information, the charge must be refreshed every 1 or 2 milliseconds by use of a Refresh circuit, which can be incorporated within the CPU.

- Since the memory chips are too small, they must be combined and put on a medium that can be worked with and added to a system. To achieve this, the designers place the memory chips on a small fiberglass card to create the SIMM (Single Inline Memory Module) or DIMM (Double Inline Memory Module).
- These cards are placed in a socket on the motherboard, and then fastened/ bolted in. This design eliminated problems of the past, and made upgrading memory a simple task.



Secondary Storage (also Called Auxiliary or Backing Memory).

  • Secondary memory is used by the computer to hold programs, data files & backup information that is not needed immediately (not currently in use) by the Processor.
  • However, contents in a secondary storage media can be quickly transferred into the computer’s Main memory for processing when required.
  • It is also used by the computer to supplement the computer’s main (internal) memory in case of mass storage purposes.
  • This storage is provided by less expensive devices such as:
    1. Magnetic disks (Hard disks &Floppy diskettes).
    2. Winchester disks.
    3.  Magnetic tapes.
    4. Cassette tapes.
    5. Punched cards.
    6.  Zip disks.
    7. Optical disks, which include CD-ROMs & WORM (Write once Read Many) disks, and
    8. Digital Video Disks (DVDs), which can be connected to the computer.
  • Most of these storage media are magnetic based, i.e., they use the principles of magnetism to store data and instructions in form of binary.
  • The data is stored permanently in Disk drives. The disk drives can either be fixed inside the computer, as in the case of Hard disks, or inserted anytime you want to read or write in them.

What is a Disk drive?

  • A Disk drive is a computer device for reading or writing data from or into a storage media.
  • A Disk drive is a hardware on which files can be stored.
  • A Disk drive is a unit that houses a disk.

    Examples;
    • Hard disk drive (HDD or drive C:).
    • Floppy disk drive (FDD or drive A:).
    • CD-ROM drive.
    • DVD-ROM drive.
    • Tape drive.
    • Zip drive.
  • A Disk drive can be used as an Input device, Output device or Secondary storage device.

Characteristics of Secondary Storage Devices.

  1. They provide slow access of information they process data very slowly compared to primary storage.
    - Modern secondary storage devices normally operate in milliseconds. It can take between 25 50 milliseconds to locate information in a disk drive.
  2. They have high data storage capacity.
    - Disks & Tapes can store large amounts of data and instructions; however, the amount of storage is limited by the no. of disk packs or tapes you buy.
  3. The devices are cheap.
  4. They are non-volatile. Secondary storage units store data permanently.
  5. Used for mass storage of data & program files not currently being operated on, but which will be transferred to the main storage when required.

Question. Identify the advantages of secondary storage devices.

The Need for Secondary Storage in Computers.

  1. The amount of storage needed on a typical Microcomputer system might be greater than the storage space available in the Main memory. This requires the use of backing storage devices, which can be used to store large quantities of information.
  2. Whatever is in memory is lost when the computer is switched off. Thus, there is a need to store programs & data in secondary storage devices from which it can be retrieved when needed.
  3. Primary storage is expensive, thus the need for secondary storage devices which are cheaper.

Functions of Secondary Storage Devices.

  1. Used to store backup data & instructions that is not needed immediately (or not currently in use) by the CPU. This helps in creating space for another data to be stored in the memory.
  2. Used for transportation & distribution of data & software, i.e., for transferring files from one machine to another.
  3. Used to back up files (keep copies of data & programs) for safe-keeping.
    - Whatever is in memory is lost (or can be corrupted) when the computer or the power supply is switched off. Disks can therefore be used to store programs & data, which can be retrieved when needed.
  4. Used to install new software.

Magnetic Disks.

  • A Magnetic disk is a round platter made of a plastic or a metal & coated with a magnetic material, which is used for storage of information.
  • Magnetic disks can be used:
    1. To store backup data that is not being used currently.
    2. To install new software.
    3. To transfer/ transport files from one machine to another.
    4. To back up small amounts of files for safekeeping.
  • Magnetic Disk storage A storage device or system consisting of magnetically coated disks, on the surface of which information is stored in the form of magnetic spots arranged in a manner to represent binary data. The data are arranged in circular tracks around the disks and are accessible to reading and writing heads on an arm which can be moved mechanically to the desired disk and then to the desired track on that disk.
  • Data recorded on a magnetic disk can be read/ retrieved in 2 ways: -
    1. Sequentially or Serially – whereby data from a given track are read or written sequentially as the disk rotates.
    2. Directly.

    Illustration.
    • Suppose there are 5 records stored on track 0, and 5 records on track 1.
    • In Sequential access/ retrieval, the records from track 0 are read, followed by the records from track 1, and so on until all records have been retrieved.
    • In Direct data access/ Retrieval, the records are accessed directly, in any order, moving the Read/write heads to the track that contains the data required.
      For example, suppose you want to read record 99, followed by record 20, then followed by record 43. If the records are located on tracks 19, 3 & 8 respectively, then the read/write head will move to track 19, then back to track 3 & then to track 8.
      - In order to read record 99, there is no need to access records 1 to 98; the head can proceed directly to where record 99 is located.
  • The storage capacities of disks are commonly expressed in terms of the no. of bytes of data they can hold.
  • A Magnetic disk can be of 2 forms: -
    1. Floppy diskettes (Soft disks).
    2. Hard disks.

Floppy Diskettes.

  • A Floppy disk is a disk that can be inserted in & removed from a disk drive.
  • The 3.5-inch disk is inserted via a slot in front of the System unit/ cabinet.
  • Floppy disk units are single-drive units able to hold a single disk. The disk unit is incorporated physically into the body of PCs. Such disk drives are called Internal disk drives.
  • A Floppy disk is made from a thin, flexible plastic circular material. The plastic material is coated with a magnetic substance (usually Iron Oxide), which enables data to be recorded on the disk.
  • The plastic disk is protected in a rigid smoothly lined plastic envelope; that safeguards the recording surface against external influences, e.g., touch and dust accumulation onto the recording surface.
  • Floppy diskettes can bend easily.
  • The diskettes are relatively cheap and conveniently handled. However, they are only suitable as storage media in Microcomputer systems because, they store relatively low volumes of data and have a short life.
  • The storage capacity is influenced by the no. of sides of the plastic base coated with magnetic material & the storage density, measured in bytes. The common storage capacities are 360, 720, & 1,440 bytes.
  • In single-sided disks, data can only be recorded on one side, whereas in double-sided disks, data can be stored on both sides.
  • The disks come in different densities. The Low density (single-sided) disks, which hold 720KB of data & High-density (double-sided) disks, which usually hold 1.44MB of data.

Uses of Floppy diskettes.

Floppy diskettes are used: -

  1. To distribute software on microcomputers.
  2. To collect or input data for subsequent transfer and input to another system.
  3. As backup media for small hard disks.

Common types of Floppy drives.

- The diskettes come in different sizes.

  1. 3.5-inch drives, which accept the small 3.5” disks.
  2. 5¼-inch drives, which accept the big 5¼” disks.
  3. 8-inch drives.

- The 3.5” & 5.25” diskettes are used in Microcomputers, while the 8” diskette is normally used in Minicomputers & Mainframe computers not for storage but as a data collection/capture medium.
- The diskettes can only be read by drives that are designed to read/write onto them, i.e., a lowdensity 3.5-inch drive will only read and write the low-density diskettes.
- However, most high-density drives are able to read and write both low-density & high-density diskettes.

floppy disk

  1. Permanent label.
    - It is incorporated on the diskette when it is bought.
    - It has on it an arrow indicating the direction of inserting the diskette into its drive, information about the diskette, such as the no. of tracks per inch, the version of the diskette, e.g., Single-sided Single density (1S1D) & the trade name of the diskette.
  2. Temporary label.
    - This is the label, which is attached onto the diskette by its user to specify, e.g. the name of the owner, name of programs maintained on the diskette, etc.
  3. Security tags.
    - Are used to safeguard the contents of the diskette. When the hole is covered by the shutter (a plastic band), the diskette cannot be written to or its contents altered.
  4. Spindle hole.
    - It is the hole used by the disk drive to hold/ clump the diskette over its turntable for the drive motor to spin the diskette past the Read/Write heads so that the reading or writing operations can be performed on the recording surface(s) of the diskette.
  5. Read/Write region (Read/write head slot)
    - This is where the diskette’s recording surface is exposed. It is used to give the heads of the disk drive access to the disk.

Comparison between 5¼-inch and 3½-inch diskettes.

  5.25-inch Floppy B: 3.5-inch Floppy A:
Densities Low-density High-density Low-density High-density
Capacity (Bytes) 360KB 1.2MB 720KB 1.44MB
Tracks 40 80 80 80
Sectors 9 15 9 18
Heads 2 2 2 2
Type Flexible Flexible Rigid Rigid

DS Double-Sided. HD - High-Density.

  • Both types are either of low density or High density.
  • The 5.25 inch diskettes are flexible, while the 3.5 inch are rigid.
  • 5.25 inch diskettes have a max. of 15 sectors, while 3.5 inch diskettes have a max. of 18 sectors.
  • The 3.5-inch disks store more data, and are better protected. They have now replaced the 5.25-inch diskettes, which are only used on existing 8088 PCs.

- The disk surface is divided into concentric circles called Tracks. The Tracks are further subdivided into Sectors, which are used for data storage. Data or information is recorded on the Tracks & sectors. Typically, each sector is 512 bytes.
- The tracks are described as concentric, because they allow the moving around one track from a given start point and end up at the starting position.

tracks and sectors

Hard Disk.

  • Hard disk is made of metal & is usually rigid/ firm.
  • Hard disk is not removable like the floppy disk, but it is fixed inside the computer. However, it works on the same basic principles as the floppy disk.
  • A hard disk is made up of one or more platters (disk plates), arranged one on top of the other to form a disk pack. The platters are made from a metallic material, usually an Aluminum alloy or Glass in order to make them light.
  • The glass platters have enough Ceramic within it to resist cracking & also they can better resist the heat produced during operation.
  • Each platter is coated on both sides with a magnetic material, usually Iron Oxide, which enables data to be recorded on the platter. This is why many platters are brownish orange in colour.
  • The mixture (of the magnetically sensitive substance) is poured on the platter, then spinned to evenly distribute the film over the entire platter.
    harddisk structure
  • The disk pack plates are held on a rotational Spindle, which is used by the drive motor to rotate the plate surfaces past the Read/write heads in order for the read & write operations to be performed on the recording surfaces.
  • Data is written on & read from the disk using Read/write heads in the disk drive, under the influence of the computer’s command signals.
  • The heads are attached to a device or an access arm called the Head Actuator, which is used to move the read/write heads across the platters to the destination track.
  • There is usually 1 Read/write head on each side of a platter & all the heads are attached to a single actuator shaft so that the heads move in unison. Each head has springs to force it into the platter it reads.
  • When off, the heads float between the surfaces of the platters, which are held in a vacuum that enables it to spin/ rotate around very quickly.
  • When the drive is running, the platters rotate causing air pressure that lifts the heads slightly off the platter surface. The disk rotates & the heads can move in & out over the surface to record or read data on the various tracks.

    Notes.
    • The Read/Write heads do not touch the disk plate’s recording surface. They fly over to avoid the R/W head’s ‘crash’, which may result in the wearing away of the magnetic coating over the recording surfaces that may cause loss of the recording property of the magnetism.
    • The distance between the head & the platter is very small such that the drive must be assembled & repaired in a very clean room because one dust particle can throw the whole drive off.

Data Storage In a Hard Disk.

  • The surface of each disk is divided into a no. of concentric circles called Tracks, each track being divided into Sectors.
  • The storage capacity of a hard disk is much higher than that of a floppy disk, & is therefore able to store much more data than a floppy disk of the same size because of technical differences.
  • The storage capacity of the hard disk is determined by the no. of recording surfaces, no. of tracks per surface & the recording density.
  • The computer identifies the record sought for by using its track no., or cylinder no. & the sector no. for its direct retrieval.

Hard Disk Access Mechanisms.

  • In order for a drive to read or write to a disc, it must be spinning at a constant speed. Floppy disk drives only begin rotating whey they are required to read or write data. However, Hard disks spin continuously, often at 3,000 revolutions per second.
  • The Read/write heads are capable of crossing the disk surface from one track to another very fast, making it possible to locate a data file or even a particular record/item within a file on the disc very quickly.

Terms used to define Access Times in Hard disks.

- The Hard disk is a Direct Access Storage Media (DAS/m). Its Access Time is obtained in same manner as that for the diskette. However, the Access Time is influenced by:

  • The arrangement of the Read/Write heads.
  • The rotational speed, which is faster than that of the diskette.

- If the disk pack is removable from the unit, the disk drive or unit is referred to as an Exchangeable Disk Unit (EDS). If the disk pack is permanently held in a unit, the disk drive or unit is referred to as a Fixed Disk Unit (FDU).
- Disk unit - is the device in which the disk pack is placed.

Features of a Fixed Disk unit.

  • The unit houses a no. of non-removable disks.
  • It has a motor that rotates the drive at a high contact rate.
  • In a Fixed-Head drive, there is usually 1 read/write head for each track on a given surface.

    For example, if there are 200 tracks per recording surface, then there will be 200 R/W heads serving each surface, such that, when accessing data, there is no head movement in reading data from one track followed by data from another track. This means that during the Read and Write operations, the R/W heads doesn’t have to move in order to locate the right track because, each track is already located, hence the seek time is zero. This implies that the access time for the disk pack of a fixed head drive is reduced.
  • Fixed head drives are more expensive than moving head drives.

Moving Head Drive.

  • The recording surface of each disk plate is supplied by only 1 Read/Write, regardless of the no. of tracks the surface contains. Therefore, during the read and write operations, the R/W head servicing the surface must move in order to locate the right track containing the contents requested.

Example:

- Suppose the R/W head is positioned over track 20 & the data required is on track 20. Then this data can be read as the disk rotates past the head.

- Suppose the data required is on track 64. Then the access arm must first move the R/W head from track 20 to track 64. Once the head is positioned over track 64, the data is then read.

  • After the head is positioned over the desired track, it has to wait for the right sector. The time taken for the disk to rotate from its present position to the position on the track at which the data starts is called Rotational delay (latency) & is measured in Milliseconds.
    - The faster the hard drive spins, the shorter the rotational latency time.
  • The time taken to read & transmit the data to the computer is called the Transmission Time.

- For a moving head drive, the time taken to access data (i.e., Access Time) usually ranges between 25 100 Milliseconds for a hard disk system & 100 600 milliseconds for a floppy disk system.

 

Advantages of Magnetic Disks.

- Magnetic disks (Floppy disks & Hard disks) are the most commonly used medium for online secondary storage in microcomputer systems because of the following reasons: -

  1. They are cheap (Low cost).
    - Although disk drives are expensive, the use of removable disk packs enables storage capacity to be increased very cheaply.
    E.g., to improve the storage capability of a floppy disk system, you simply need to buy additional disks at low cost.
    - The cost of Hard disks has decreased making them to be widely used on microcomputers.
  2. Have relatively fast access times for data stored anywhere on the disk.
    - For hard-drives, the data Transfer rate between memory & disk is 300,000 2 million characters per second, while that of floppy disks is between 30,000 150,000 cps.
  3. Have high storage capacities.
    - Hard disks can store tens of millions to hundreds of millions of characters while floppy disks can store between 100KB 2 MB of data.
  4. They are re-usable - the disk space can be re-used by simply recording new data over old data. Also, the data stored in a magnetic disk can be easily corrected or updated.
  5. They are Non-volatile - information is stored permanently.

Disadvantages of Magnetic Disks.

  1. Data stored on magnetic disk is not human-readable, i.e., to verify the accuracy of data stored on the disk, a computer run has to be made, which reads the contents on the disk.
  2. A disk is susceptible (prone) to dust, stroke & magnetic fields; which can distort (deform/disfigure) data on the disk causing disk-reading errors.
  3. Require enough skills to manage the disks effectively.

Differences between Hard disks & Floppy diskettes.

Floppy diskette. Hard disk.
1). Can be inserted in & removed from a disk drive. It can also be transferred between computers.
2). Made of a flexible plastic material & can bend easily.
3). Consists of a single platter/ disk.
4). Cheaper.
5). Floppy disk drives only begin rotating when they are required to read or write data.
6). Have a spindle hole.
7). Low storage capacities compared to hard disks, e.g. a Floppy disks store between 100KB – 2MB of characters.
8). Slower access times, e.g. the data transfer rate between memory & the disk is between 30,000 – 150,000 characters per second.
1). It is not removable like the floppy disk, but permanently housed in a disc unit inside the computer.
2). Made of a metal & is usually rigid/ firm.
3). Made of more than 1 platter arranged one on top of the other to form a disk pack.
4). Relatively expensive than floppy disks.
5). Hard disk drives spin continuously, i.e., they start rotating when a computer is switched on.
6). Have a rotating spindle that holds the disk plates together in a disk pack & is used to rotate the disk pack when reading or writing onto the disk.
7). Hard disks have a much higher storage capacity than floppy disks, e.g. can store between 10 - 80 million characters.
8). Have faster access times for data stored in it than a floppy disk, e.g. the data transfer rate between memory & the disk is between 300,000 – 2 million cps.

Zip Disks.

- Zip drives act as either external or internal devices.

  • The Zip disk is found in a hard plastic case, and like the diskette, it uses a magnetic material for double-sided recording & reading.
  • Zip drives are larger & their read/write heads can operate more efficiently than those on a regular floppy disk drive.
  • Zip disks are usually portable.
  • Each disk can hold up to 100 MB.

Magnetic Tapes.

  • These are the storage media mostly used in Mini and Mainframe computers.
  • A Magnetic Tape reel is made of a plastic ribbon/ band coated on one side with a magnetic material that enables data & instructions to be recorded/ stored on the tape.
  • Magnetic Tape a tape with a magnetic surface on which data can be stored by selective polarization of portions of the surface.
  • The reels of the Tape are stored in a protective case, which safeguards the recording surface of the reel from environmental destructions, e.g., touch, dust, direct sunlight radiations, etc.
    magnetic tape
  • Usually, a plastic ring (the Permit ring) is affixed on the Permit Ring Groove, which is on the case, before the tape is mounted in its deck. The Permit ring is used to protect/ safeguard the contents of the tape.
  • If the permit ring is affixed, the tape surface can be written to & read from, hence it is possible to alter the contents of the tape. If the permit ring is not affixed onto its groove, the tape surface can be read but cannot be written to; hence the tape user cannot alter the tape contents.
    tracks magnetic tape
  • The width of the tape is divided into Tracks, while the length is divided into vertical columns called Frames. Each frame is made up of 7 storage unit areas (bit positions). These frames are used to store individual characters across the tape width.
  • The recording surface of a tape has 7 or 9 tracks running along its length. Each recording position on a track can be magnetized to represent a ‘1’, while that which is not magnetized represents a 0. Thus for a 9-track tape, each frame contains 9 bits & is used to represent 1 character.
  • A tape is usually ½ (0.5) inch wide & 2,400-feet long. The characters are recorded across the tracks on the tape.

Advantages of Magnetic Tapes as secondary storage medium.

  1. Tapes have a high storage capacity (or high data recording density), i.e. they can store lot of information in a small space.
    - Usually 1-inch of the tape can store between 1,600 6,400 characters. This also means that, a tape can allow a complete hard disk to be backed-up without the need to change media during the process.
  2. Tapes are cheaper compared to other removable storage media.
  3. Have high data transfer rates.
    - Reels of a magnetic tape have a transfer rate of approx. 10,000 1 million cps, whereas in cassette tapes, the transfer rate is about 1,000 cps.
  4. Tapes are re-usable. When information on a tape is no longer required, it can simply be written over’ with new information.
  5. The domestic cassettes can also be used as storage media in small home computers where the speed of retrieval is not a necessity and the volume of the capacity of the cassette is enough. This is because domestic cassettes operate on the same principles as the magnetic tapes.

Disadvantages of storing records on Magnetic Tapes.

  1. Data stored on a tape must be read/ accessed sequentially, one record after another. E.g., if you need to update the 100th record, all the previous 99 records must be read, pass under the Read/Write head (or at least skipped over) to reach the record the user is searching. Hence, slow data, instruction and information retrieval.
    - This means that, if you need to process records in a different order, let say, record 100 followed by record 5, followed by record 50, the processing would be slowed down a lot because the tape would have to move back & forth. However, if the records have to be processed in sequence, i.e. from the first to the last, it would be fast.
  2. Data stored on magnetic tape (& disk) is not human-readable.
    - E.g., if you wish to verify the accuracy of data stored on the tape, a computer run would have to be made, in order to read the contents on the tape and print it.
  3. Tapes have short life spans (average of about 2 yrs).
  4. A tape is susceptible (prone) to dust, stroke & magnetic fields; which can distort (deform) data on the tape causing tape-reading errors.
  5. Tapes do not fully use their recording surface.
    - An inch of tape may hold 1,600 - 6,400 characters & the IRG may be 0.5-inch. This means that, almost a of the unused space on the tape is wasted.

Magnetic Tape Cartridge & Cassette Tapes.

  • They operate on the same principle as ½-inch reel-to-reel tape.
  • The domestic Cassette tapes are very similar to magnetic tapes. The only difference is that
  • Magnetic tapes are wider & longer than the domestic cassettes.
  • Many cartridges are designed to overcome the bother of loading and unloading tapes.
  • A tape cartridge gives greater protection against dust & dirt and then makes the tape trouble-free.
  • Tape cartridges provide an effective way to copy the contents of disks to guard against data loss.
  • On cassettes tapes, characters are stored serially down the length of the tape, one at a time. This slows down the processing speed of the information stored on the tape.

Advantages of Cassette Tapes.

  1. They are very cheap & convenient, making them to be a widely used form of secondary storage in many home computers.
  2. It can store hundreds of thousands of bytes of data.
  3. Can be re-used.
  4. An ordinary cassette player can be used to record & play back the data on the tapes. Therefore, no expensive Input/Output device needs to be bought.

Comparison Between Magnetic Disks & Magnetic Tapes.

Similarities.

  1. Both are coated with magnetic materials.
  2. Have high data storage capacities, i.e. can store hundreds of thousands of bytes of data.
  3. Have high data transfer rates.
  4. Hold data permanently, i.e. are Non-volatile.
  5. Cheap and convenient; hence, the reason why they are mostly used for secondary storage in PCs.
  6. Require drives in order to read or write data from or into a disk or tape.
  7. Data stored a magnetic tape & disk is not human readable, i.e., to verify the accuracy of data stored on the tape or disk, a computer run would have to be performed.
  8. Both are adversely affected by dust, stroke & magnetic fields, which can distort data stored in them causing data reading errors.
  9. Tapes or disks do not fully use their recording surfaces. The Inter-Block Gaps in tapes occupy a large space; while in disks, a space has to be left for purposes such as copying & moving of files, defragmentation of the disk, etc.
  10. Both tapes & disks are re-usable. When information on a tape or disk is no longer required, it can simply be “written over” with new data.
  11. Data in them can be read sequentially, e.g., when playing music or watching a movie on a disk.

Differences.

Magnetic Tape Magnetic Disk
1). Consist of a strip of plastic, i.e., reels of tape.
2). Only 1 side of the tape is coated with a
magnetic material for recording data.
3). 1 track of the tape is not used for data 
storage, but for parity check, i.e., to 
ensure that data recorded & transmitted is accurate.
4). Requires tape drives to write information 
to & read data from the tape.
5). Data is stored on a tape in form of 
records that are organized in blocks.
6). Have Inter-Block/Record Gaps (blank spaces)
separating two successive blocks or records.
7). The records on a tape are read
sequentially, i.e. one record after another 
in the order they occur on the tape.
8). Data is recorded across the tracks on the 
tape or serially down the length of the tape.
1). Consist of round platters made of plastic or metal.
2). Both sides of the platters can be coated
with a magnetic material for recording data.
3). The whole disk surface can be used for
recording data. However, in hard disks, 
the top most surface of the 1st plate & 
bottom most surface of the last plate are 
not used for recording data as they can easily be scratched.
4). Require disk drives to read or write data in the disks.
5). Data is stored on the disks in files, folders or directories.
6). Have no blank spaces between the tracks 
on the recording surfaces. However, they 
use a recording method known as 
Tunnel Erasure;
which is used to keep each track 
of data separate from the others.
7). Data recorded on a disk can be read sequentially or directly.
8). Data is recorded on concentric circles on 
the disks called 
tracks.

Punched Cards & Punched Paper Tapes.

  • These are paper media, which were used as storage media by the early computers.
  • They been replaced by the magnetic media, due to the following reasons:
    1. They are bulky.
    2. Provide slow input.
    3. They are non-reusable.
    4. They can be destroyed due to dust.
    5. Costly to produce - the punching & verification are tedious and expensive.

Optical Disks.

  • Optical disks use Lasers to read or write data. When writing, a laser beam is used to align a permanent data pattern on the disk surface. When reading, the data contents are sensed by the pattern of light reflected from the beam by the data on the disk surface.
  • There are 2 types of Optical disks:
    1. CD-ROMs (Compact disc Read-Only Memory)
    2. WORM (Write Once Read Many) discs.

CD-ROMs (Compact Disc Read Only Memory).

CD-ROM (Data CD)

  • A CD-ROM (also known as a data CD) is a compact disc used to store computer data.
  • CDs (Compact discs) were originally developed for the music industry. They use small disks identical to the ones that hold music to hold computer information.
  • They have higher storage capacities than traditional Magnetic disks.
    - The current CDs can hold about 650 MB of data compared to the 3.5” floppy diskette, which can only hold 1.44 MB of data.
    - This storage capability enables programmers and other data distributors to write more sophisticated programs for computer users, because they are no longer limited by data storage space.

The CD-ROM Technology

  • A CD is made by having information burnt into the Polymer material using a laser. The indentations appear as fine circular tracks in the CD.
  • Data is written on the CD in a continuous spiral running from the center of the CD to its outside rim. All the bits in a file are written one after the other from beginning to end, then the next file is written, and so on.
  • A logical format (or file system) structures the raw bits on the CD in a virtual tree of directories and files, which makes it easier for both humans and computers to use the information.
  • ISO 9660 is a worldwide standard specifying the logical format for files and directories on a CDROM.
    CD ROM
  • To use the CD-ROM discs, a CD-ROM drive is needed.
  • The devices in a CD-ROM drive are only able to read back pre-recorded sound or data by using a laser and detecting the pattern of light reflected from its beam.
  • The current CD-ROM drives use Multi-session & Multi-speed technologies due to the intense requirements of most multimedia applications. The Multi-session technology allows data to be written to a CD again & again until it reaches its maximum capacity (650MB).
  • The Multi-speed technology increases the rotational speed of the disk, thus increasing the data transfer rate of a CD-ROM drive.

Uses of CD-ROMS (CDs).

Typical uses for CD-ROMs include:

  1. Archiving data.
  2. Backing up a hard drive or other media.
  3. Creating a test copy of a CD before having it factory-duplicated.
  4. Disseminating information to field offices.
  5. CDs are the primary methods of installing software.
    - Most software companies distribute application software in CD-ROMs.
  6. CDs are used in Multimedia (the integration of text, motion video, graphics, & sound).
    - Programmers pack Multimedia in the CD-ROMs enabling consumers to enjoy the work of multimedia inventions.
  7. To provide reference works, catalogues, directories, encyclopedias, software front descriptions, graphical images and sound.

Types of Compact Discs:

There are 2 types of Compact Discs (CD-ROMs): -

  • CD-Recordable (CD-R) discs.
  • CD-ReWritable (CD-RW) discs.

CD-R (Recordable).

  • A CD-R holds data permanently, i.e., once written, it cannot be erased or overwritten.
  • CD-R can be used to store or backup a lot of data (about 650MB), thus making it suitable for businesses that need to record/ store a lot of information.

Advantages of CD-R

  1. Good for permanent data storage.
  2. Less expensive per disc than CD-RW disc (CD-R discs are cheaper compared to CD-RW).
  3. Readable on virtually all CD-ROM and CD-R drives.
  4. Use when you do not need to erase the data.
  5. CD-R drives can write faster than most CD-RW drives.

Disadvantages of CD-R.

  1. The disc can only be written once, (i.e. once something has been recorded on a CD-R, it can’t be erased or written over again).
  2. The future of CD-R drives seems to be in doubt since CD-RW drives can accomplish the same thing as CD-R drives.

Note. In a CD-R drive, there are 2 speeds listed.
- The faster of the two speeds is the speed at which the drive reads information from a disc, while the slower one is the speed at which the drive records information onto a CD-R

CD-RW (ReWriteable).

  • It is possible to record data on a CD-RW more than once. With CD-RW drive you can also erase the contents of a CD and re-write new information to it.
  •  In addition, CD-RW drives can play audio CDs, use the regular CD-ROMs & read CD-R discs.
  • This makes CD-RW drives very desirable.
  • Most CD-RW drives can also record to CD-R discs, making it possible to use CD-R discs with a CD-RW drive.

Advantages of CD-RW.

  1. Used when you need to erase the data and re-write new information (e.g., updating files). Data written to a CD-RW is not permanent, i.e. it can be overwritten or erased.
  2. Used to make a practice CD or to test the contents of a CD before making a permanent one.
  3. More cost effective for near line data storage requirements than CD-R.

Disadvantages of CD-RW.

  1. CD-RW drives & media are expensive/more costly than CD-R drives.
  2. CD-RW are slower than CD-R & CD-ROM drives. It takes about 1hr to format CD-RW discs & about ½ an hour to copy 250 MB of data to the disc, while CD-R discs take a few minutes to format and have the same write time.
  3. Data can be read and written to CD-RW discs only by CD-RW drives.
  4. CD-RW drives are currently facing stiff competition from the DVD-Recordable (DVD-Rbecause the DVD-R can store more information than CD-RW.

Note. Both CD-RW & CD-R can be read by standard CD-ROM drives.

WORM (Write Once Read Many) discs.

  • A WORM disc looks like a CD. Also, data is read from the disk in a similar way to that on a CD.
  • The WORM disc surface has 40,000 Tracks, 25 Sectors and a total storage capacity of 1GB.
  • Data is written into the disc by burning a permanent pattern into the surface of the disc by means of a high precision laser beam.
  • The WORM discs are exchangeable.
  • WORM discs are non-erasable & are less prone to data loss compared to Magnetic disks.
  • Access speed of a WORM disc is slower than that of Magnetic disks.
  • To use the WORM discs, a WORM disk unit/drive is needed. The drive is similar to magnetic disk unit.
  • An example of a WORM drive is the CD-R, which uses the same size of disks as CDs and once written using the CD-R drive, it can be read in a CD-ROM disk drive as well as in a CD-R drive.

Uses of WORM disks.

  • WORM drives store large amounts of data.
  • They are used to put data online for reference purposes.

Advantages of Optical discs as secondary storage media.

  1. Have very high storage capacities. This enables them to be used for multimedia applications.
  2. Have relatively high access speeds.
  3. Are Non-volatile, i.e. information kept in them is permanent. Therefore, they are more secure against alteration.
  4. Are cost effective (cheap) especially if used for large storage volumes.
  5. They are robust they resist temperature, electromagnetic fields, and not affected by water or dust.
  6. Have very high data transfer rates.
    - Modern CD-ROM drives have data transfer rates of between 150 4,800 KB/second.
  7. Some Optical discs allow data to be written to them a no. of times, e.g., CD-RW.

Reasons why Optical discs (CD-ROMs) are not mostly used in microcomputer systems as secondary storage media.

  1. CD-ROMs require special writers to write to the disk. The CD Writers are usually expensive, thus limiting the utility/ usefulness of CD-ROMs as computer storage devices.
  2. Are expensive (not economical) especially if used for low storage volumes.
  3. Require CD-ROM drives to use the discs, which are not installed on most desktop computers.
  4. Most CD-ROMs are produced by the manufacturer or can only be written once. Therefore, they are not reliable especially for businesses that may need to re-programme the CDs to suit their needs.
  5. Are slow to prepare, i.e., it takes time to format & also to copy data into the discs, e.g. CDRW disks take about 1hr to format & about ½ an hr to copy 250 MB of data to the disc.
  6. The Access speed of an Optical disk is low.

DVD (Digital Video Discs).

  • A DVD looks like a CD-ROM. However, a DVD can store much more information.

    For example:
    • A single-sided DVD can hold 4.7 GB of information (a 133 minutes of full-motion video), while a double-sided DVD can hold 17GB of information (the equivalent of 8 hrs of studio quality video); enabling most movies to be stored on a single disc.
  • This amount of storage gives software programmers flexibility when it comes to designing programs. They are able to store all the high-quality graphic images, digital sound & tools they want in a single DVD.
  • Currently, DVDs are used primarily for movies. The DVD videos offer superior pictures & sound, the ability to play audio CDs in a DVD player, and pictures that are sharp & clear than VHS videotapes.
  • To use a DVD, your computer should have a DVD-ROM. To read the DVD-ROM, a DVDROM drive is required.
  • In order to enjoy all the functionality of a DVD, the computer must have a Motion Picture Expert Graph (MPEG) decoder card or MPEG software. This enables the user to view full screen video or video clips from a DVD video disc.
  • DVD drives are reasonably/ fairly priced.
  • DVD drives can read all other ROM formats - audio CDs, CD-ROMs, CD-R, CD-RW & DVDROM discs.
  • The current DVDs are not recordable, i.e. they don’t have the ability to record information.

Handling Precautions For Magnetic Media.

  1. Should be stored in optimum temperature ranges, e.g. 10oC 52oC for diskettes.
  2. Should be protected in their cases when not in use in order to safeguard their recording surfaces against environmental influences such as dust, touch, direct sunlight, radiations, etc.
  3. When loading/ mounting the media into its reading/writing unit, care should be taken to avoid brushing the recording surfaces against the mechanical components of the drive.
  4. Should never be brought near moving or magnetic bodies. Such bodies might cause the demagnetization of the recording surfaces (i.e., remove the magnetic property from the surfaces) making recording in terms of magnetism impossible.
  5. Put on the power before mounting the media and off after removing the media from the drive. This is because the fluctuation in power might also cause de-magnetization.

Physical storage considerations.

  • Recording density The no. of useful storage cells per unit of length or area.

    For example,
    - The no. of characters per inch on a magnetic tape or punched card.
    - The no. of bits in a single linear track measured per unit of length of the recording medium.
  • Volume - A term used for any individual physical storage medium that can be written to or read from. E.g., a fixed hard disk, floppy disk, CD-ROM, a disk cartridge or tape cartridge.
  • Formatting - Before a diskette can be used, it must be formatted. This prepares the disk so that the drive can use it.
  • Initialization - Before a disk is recorded, it has to be initialized, i.e., writing zeros to every byte on every track. This eliminates all trace of any existing data.
  • Fragmentation - When data is written on a newly formatted disk, it is usually written to unused contagious sectors. If data is erased, then the deleted sectors may leave spaces among used sectors. Overtime, after many inserts and deletes, these free sectors may be scattered across the disk. In such a phenomenon, the disk is said to be fragmented.


Output Devices

  • When the computer processes the data (or after the computer finds the solution to the problem), it displays the results (or communicates the solution to whoever posed the question) by use of an Output device.
  • The term Output is used to describe all that comes out, from the computer memory, or from the processing stage of a data processing system to the external environment.
  • Output therefore, involves receiving information (processed data) from the computer through a suitable device for external use.
  • An output device provides the user with the results from the computer.

Functions of Output Units.

  1. Transmit the intermediate results & final results to the users.
  2. Convey messages, e.g. error messages, to the operators.
  3. Provide immediate response to queries/ questions.
  4. They are used when writing onto the secondary storage media.
  5. Accept the results produced by the computer (which are in coded form & hence cannot be easily understood) & convert these coded results to human readable form.

- The output produced by computers can be put into 2 broad categories: -

  1. Human-readable output, which serves the informational needs of people. This is a form of output that is readily understandable by human beings, e.g., printed or drawn output.
  2. Machine-readable output, which is required/used for subsequent input to the computer.
    - In this case, the output may be temporarily stored on machine-readable media.
    For example,
    - In the production of a payroll for a company, a payroll report is produced listing the amount each employee must be paid. This report can then be used by the person responsible for issuing cheques.
    - At the same time, an updated employee file is produced, say, on a tape. The tape will be used as input to the computer for the next payroll run.
    - The quality, validity and usefulness of the output is influenced by the output facility used.

The following factors/ considerations determine the choice of output equipment and media.

  1. Suitability of the application.
  2. The speed at which the output is required.
  3. Whether a printed version is required.
  4. The volume of the data.
  5. Cost of the method chosen as compared with the benefits to be derived.

Divisions of Output.

Output can further be classified as: -

  1. Hardcopy output.
  2. Softcopy output.

Softcopy Output.

  • This is where the end results are displayed on a screen. The user can see the results, but cannot touch them.
  • The output lasts for a short-time only, i.e., it is available only as long as it appears on the screen.

Examples of Softcopy Output devices.

  • Visual Display Units (VDU) / Monitor.
  • Audio Response Units.
  • Speakers.

Hardcopy Output.

  • Hardcopy implies that the output is permanent, i.e. it can be retained for an indefinite period.
  • The user can see & touch the results.
  • Hardcopy is desirable if the information or the results of the computer working is to be maintained for future reference/ use.

Examples of Hardcopy Output devices.

  • Printers.
  • Graph Plotters.
  • Microforms.

Visual Display Unit (VDU)/ Monitor.

  • Visual display unit (or a Monitor) is a television-like screen, which displays the data that is being typed at a Keyboard. It also displays the information that has been processed by the computer in a human-sensible form.
  • In many cases, an ordinary television set can serve as the display unit.
  • The display is meant to provide a means of visually checking whether the information that has been entered is correct.
  • The output displayed on a monitor screen is called a Softcopy output

Classes of Monitors.

  1. Cathode Ray Tubes (CRT) found in most desktop microcomputers.
  2. Liquid Crystal Displays (LCD) used by Laptops and Notebooks.
    - The resolution of a CRT is adjustable, while that of an LCD is often set.
    - The CRT can display an almost unlimited no. of colours, but the LCD can display a limited no. of colours.
    - LCD’s are backlit by a series of light bulbs. Notebooks use only 1 light bulb in order to conserve power, but desktop LCD’s can use up to 4 bulbs. These bulbs can be replaced by the user. They also have a life span. Therefore, after sometime, you will notice that the screen starts becoming dimmer. Take the LCD to the vendor for a bulb.

Advantages of LCD over CRT.

  1. The screen of a LCD is much thinner & smaller than of CRT. LCD screens come in 14 or 15-inch sizes. A 15” LCD has a 15” viewable screen; a size that is only slightly smaller than a 17” CRT.
  2. LCD’s have no flicker.
  3. They consume low power than the CRT.

The performance of a computer Monitor depends on 3 factors: -

  1. Size of the screen.
  2. The number of colours it can display.
    • Monochrome monitors - display only 1 type of colour (Black for Background & White for Foreground).
    • Colour monitors - display a variety of colours.
      Examples; Enhanced Graphics Adapter (EGA), Video Graphics Adapter (VGA), Super Video Graphics Adapter (SVGA).
      - The higher the no. of colours displayed, the more realistic the images.
  3. The Screen resolution (or sharpness of the image), which is determined by the no. of pixels.
    The Viewing angle - the picture appears clear when viewed straight on or a certain amount of degrees off the center; but when you are too far over to the side, the picture grows too dim to see.

- A VDU can be used to display lines of text as well as graphics (images, pictures & drawings).
- When used for output of text, a typical display unit is made of 24 lines; each line consisting of between 40
80 characters. 
- When used for output of Graphics, the screen is considered to be composed of a no. of dots arranged in rows & columns.
- Each dot is called a Picture element (or Pixel).
- A Pixel is a screen dot & is a direct mapping of the information (e.g. character) in the Video RAM contained in the monitor’s Adapter card.
- To display an image on the screen, the selected pixels are brightened or darkened.
- The term Resolution is used to describe the no. of pixels per unit area of the screen. E.g., the no. of pixels per cm2.
- If there are few pixels per unit area, the display is said to be of a Low-resolution. If there are many pixels unit area, we talk of High-resolution display.
- The higher the screen resolution, the finer & the higher the no. of different images that can be displayed.

Note. Specific applications require certain resolutions to be able to run, e.g., Microsoft Windows.

More About Monitors & Display Adapters.

  • Monitors do not have a direct impact on the performance, but have a significant impact on the use of a PC. A bad quality monitor can hinder the use of an otherwise high-tech PC.
  • Display Presentation of information such as by projection on a screen, an Audio message, a computer print-out, etc.
  • Display Adapter Card (also called Video Card or Graphics Card).
    - The real brain of a display operation is the Video Card. It is inserted into the slot on your computer’s motherboard as an expansion card. It then speaks to the monitor about what the computer is asking it to do.
    - The Video card determines how fast graphics display, how many colours can be used, etc.
    - For a Monitor to work to its best, it must be fitted with a Video card capable of bringing out the best in it.
    - The Video Card receives image data from the Processor in form of digital information & stores it in video RAM. The digital information is then converted into analogue display signal, which is fed to the monitor.

How a Monitor Works.

  • The inner surface of the screen is coated with a Phosphorus material that emits/ produces light when struck by an electron beam. Whenever the electrons hit the phosphor, it glows, producing images.
  • When the Monitor is plugged into the Video card, it gets a scan frequency (or a signal) giving the timing of the screen redraws.
  • The electron beam must cross the screen in synchronization with the scan signal of the Video card. The beam starts at the top left of the screen, crossing to the right. As it does this, it excites the phosphor dots. On reaching the right side of the screen, it returns to the left side in order to refresh the line of pixels underneath the first one. It continues this process down the screen, returning to the top to do it over again when it has finished the entire screen.
  • During the process, the beam excites those phosphor dots, which the video card tells it to.
  • Therefore, the card gives instructions to the electron gun to excite some pixels; hence, forming pictures.
  • On a Colour monitor, each pixel contains 3 separate dots, one for each of the primary colours of light; Red, Yellow, & Blue. Combining these colours together produces the range of colours that we all know.

Screen burnout.

  • This is a term used to describe the damage caused to the inner surface of the screen display.
  • Inside the Monitor, an electron beam is aimed at a Phosphor-coated screen. If a screen display is static, the electron beam continually strikes the same place on the screen surface, and eventually burns a hole in (or wears away) the Phosphorus coating. This might take several days or weeks to occur.
    Note. Damage to the screen cannot be repaired. The damage is visible by turning & inspecting the screen surface closely. If an image can be seen, then the screen has suffered damage (i.e. it has burned out).

Factors that determine how severe the screen burnout is.

  1. Type of Phosphorus coating used on the screen’s inner surface.
  2. Length of time the screen image remains constant.
  3. The brightness & contrast of the screen.

How to avoid screen burnout.

Screen burnout can be avoided by applying the following common sense principles: -

  1. Switch the Monitor off, if you wish to be away over long periods.
  2. Turn down the screen brightness, if leaving the machine unattended.
  3. Using a “Screen Saver” program.

Types of Monitors (Displays or video Adapters).

  1. Colour Graphics Adapter (CGA) display.
    - This was the original type of Monitor, but now it is obsolete.
    - It supported colour, but could only display a limited no. of colours. Usually, it supported 4 colours at a time.
    - It also ran at a low graphics resolution of 640 x 200 pixels.
  2. Enhanced Graphics Adapter (EGA) display.
    - It is a low-grade adapter. It was developed to improve the capabilities of CGA.
    - An EGA display works with a 9-pin connector and an EGA video card.
    - They have a resolution of 640 x 350 pixels, which is better than that of CGA monitors.
    - They also offer two brightness levels for each primary colour dot, thus, displaying a wider range of colours. EGA screens can show 16 different colours.
  3. Video Graphics Adapter (VGA) display.
    - It was introduced by IBM in 1987 for use on earlier IBM PS/2 systems. The VGA Video card contains all the circuitry needed to produce VGA graphics, and like all expansion cards, it plunges into a slot on the motherboard via an 8-bit interface.
    - VGA is able to display photographic quality images on a PC, i.e. it offers clean images at higher resolutions. It is able to build an image that is 640 x 480 pixels in size.
    - With a VGA, a PC has to deal with 640 x 480 x 3 bits every time a picture changes.
    - The standard VGA can produce about 256 colours at a time from a palette of 262,144 colours.
    - The VGA can also be used in Monochromes. It is able to translate colour graphics into graphics using 64 different shades of grey. This, in effect, simulates colour on a monochrome monitor.
    - VGA video card requires a VGA monitor, or a monitor capable of accepting the analog output of a VGA card.
  4. Super Video Graphics Adapter (SVGA) display.
    - SVGA is much more advanced than VGA.
    - In most cases, one SVGA card can produce millions of colours at a choice of resolutions. It is able to show 256 colours at a resolution of 1024 x 768 pixels. SVGA is able to support 1024 x 768 x 3 bits potentially changing 50 times per second.

    Note. EGA, & VGA monitors are not interchangeable. A VGA monitor won’t even plug into a CGA or EGA card. A SVGA monitor is not supposed to work with a standard VGA card.

Advantages of VDU/ Monitors.

  1. The speed of output is fast a Monitor displays the output almost instantly/ immediately.
  2. It displays the information enabling the operator to visually verify/confirm if the data is correct.
  3. Enables the operator to monitor his/her performance & improve productivity.
  4. Used when saving the information to a secondary storage media.
  5. Minimizes paper work, hence reducing the cost incurred on stationery.
  6. Hardware costs are minimal since no extra equipments are needed as long as the VDU is available. The screen is cheap, if bought as individual device.

Disadvantages of VDU.

  1. Produces softcopy output, i.e., the output is temporary & can get lost when the power is switched off.
  2. It is impossible to produce multiple copies.
  3. It causes fatigue to the user’s eyes, especially when stared at for a long duration.
  4. Can lure computer operators into not keeping hardcopy records.
  5. Screen might not allow the viewing of the full area of data.

Factors to consider when selecting/ buying a Monitor: -

  1. Compatibility with the adapter card: The monitor must be capable of displaying the pictures that the display adapter card can generate. Otherwise, the display will be unstable.
    - The Video card must be compatible with your computer’s bus.
  2. Memory: You should have at least 2 MB of Video memory, but if you have a larger monitor, start with 4 MB of memory. Look for a video card that has room for expansion in the future in case you have to buy a larger monitor.
  3. Monitor size: This is the distance diagonally across the face of the monitor. The larger the monitor size, the more the viewable picture area.
  4. Resolution and Refresh Rate: Both features depend on each other. They work hand-inhand to produce a clean image. 
    - Refresh Rate (sometimes referred to as Scan Rate) is the no. of times per minute that a computer screen image is renewed (or the rate at which each pixel on a screen is re-drawn).
    - The Refresh Rate is measured in Hertz (Hz).
    - Make sure you know the refresh rate of your monitor. The recommended refresh rate is 60 Hz & above. The higher the refresh rates, the better.
    - A low refresh rate results in an image that flickers (shines unsteadily), resulting in eye-strain.
    - The standard for flicker-free images is 85 Hz. To detect flicker, look slightly above or to the side of the monitor. Sometimes, it helps to be in a darker room.
    - Your Video card plays an important role in all this. If your card cannot provide support for the resolutions and refresh rates of the monitor, the picture will look degraded. When pairing a video card with a monitor, at least make sure that it is capable of delivering a 72 Hz refresh rate at any resolution supported by that monitor.
    Note. In order to stop images fading on the screen, they must be refreshed (sent to the screen) at least 50 times per second. Each pixel on the screen has 3 bits of information (corresponding to Red, Green, & Blue) attached to it, and all of them have to be redrawn at high speed.
    - The higher the resolution, therefore, the more strain is placed on the performance of the monitor’s Adapter card.

Voice Output Devices (Audio Response Units -ARU).

  • An ARU converts data/ information from the computer memory (which is in electronic form) through various specialized additional circuitry into waveforms/ sound for the receiver to hear.
  • The sound can be spoken language, musical notes or beeps. This output is obviously Softcopy.
  • Voice output is useful where reading is not necessary or is impossible and where fast output is required.
    For example, Voice output is used:
    • As a learning aid.
    • In emergency situations for messages.
    • In answering services, e.g. Post office talking clock.
  • When an ARU is used to produce speech, it is called a Speech Synthesizer.
  • A Speech synthesizer is a useful form of output especially when communication with a computer is made using telephone lines. A user dials the computer & makes an inquiry. The computer output is passed through the Speech synthesizer, which is located near the computer. The output is converted to a spoken reply, which is sent to the user over the telephone line.
  • Speech synthesizers are being included in many consumer products. For example,
    • A Bathroom scale with a synthesizer can tell a person his weight, and whether he has gained or lost weight.
    • In Cameras, they can tell you if your film or exposure is set wrongly.
    • A washing machine with a synthesizer can tell you if and when to add more detergent, or the fabric conditioner.

Advantages of Voice Output.

  1. It is very fast, making it useful in emergency situations to relay messages.
  2. Can be used for distant communication, especially if done over Telephone lines.
  3. Useful where reading is impossible - can be used by visually disabled people.
  4. Errors are easily corrected. For example, when used in a washing machine, it can tell you if and when to add more detergent, or the fabric conditioner.

Disadvantages/ Limitations of Voice Output.

  1. The output is not permanent.
  2. It may be boring, especially for prolonged output.
  3. Cannot be used by people with hearing problems.
  4. If the message is conveyed through beeps, it may be hard to understand.

Printers.

  • A Printer is an output device that facilitates the transfer of information from a computer to a paper. It is used when a permanent record of the output may be needed on paper.
  • Printed output is usually referred to as Hardcopy output, which means that the document can be kept indefinitely for future reference or use. The printed output can be distributed conveniently to reach the recipients of such information/results.

Classification Of Printers.

Printers are basically classified in 3 ways: -

  1. In terms of Print speed.
    - Low-speed.
    - High-speed.
  2. According to the amount of text it can print per given period of time.
    - Character Printers.
    - Line Printers.
    - Page Printers.
  3. The method used to produce the characters on the stationery/ paper.
    - Impact Printers.
    - Non-impact Printers.

classification of printers

Character (serial) Printers.

  • Character printers are usually low-speed printers that print 1 character at a time.
  • Are comparatively slow & less costly than Line or Page printers.
  • Have printing speeds that vary from 10 to over 200 characters per second (cps).
  • They usually use the Daisy wheel or Dot-matrix printing mechanism.

Line Printers.

  • They usually print one whole line at a time.
  • Are more expensive than the Character printers, but less costly compared to the Page printers.

Page Printers.

  • Print 1 whole page at a time.
  • Are faster & relatively more expensive than both Line printers & Character printers.
  • Page printers are Non-impact printers, i.e. there printing operation is silent.
  • They provide high quality outputs.
    E.g. Laser printer.

Basic Methods Of Producing Print.

  1. Impact or Non-impact printing.
    Impact printers.
    - An Impact printer works like a typewriter where a piece of metal or plastic with a raised letter strikes an inked ribbon against a sheet of paper, leaving an image of the letter on the paper.
    - Each character print is provided by an appropriate character symbol on the print head element.
    - The inked ribbon lies between the printing head element & the paper, so that the ribbon ink can be used to pass the character images on the print-head element onto the stationery during the print head hit impact.
    - Note. Impact printers can further be classified as Character or Line printers.

    Non-impact printers.
    - In Non-impact printers, the print-head element does not come into contact with the stationery/ paper.
    - They use Thermal, Chemical, or Electrostatic principles to produce the characters on the paper.
    - They need special papers.

    Comparison between Impact & Non-impact printers.
    Impact Printers Non-impact Printers
    1. Use Inked ribbon.
    2. Slow.
    3. Able to produce multiple copies by use of
    carbon papers.
    4. Cheaper.
    5. They are noisy because the character to be
    printed is pressed against an inked ribbon
    onto to the paper by a print-head element.
    1. Use thermal or electrostatic principles.
    2. Faster.
    3. Almost impossible to produce multiple
    copies.
    4. Costly due to the technology involved.
    5. Printing operation is silent because there is
    no print-head element hitting against the
    stationery.
  2. Dot-matrix or shaped-character printing.
    - Dot-matrix printers produce each character by printing the appropriate dot combination. 
    - Shaped character printers produce each character by use of the whole character symbol just like as in an ordinary typewriter.

Print speeds.

  • The speed of a printer is expressed in Characters per second (cps), Lines per minute (lpm), or Pages per minute (ppm).
  • There are basically 2 types of printers: -
    • Low-speed printers.
    • High-speed printers.
  • Each type is then classified further based on the technology used for producing the output & the amount of text it can print per given period of time.

Low-speed Printers.

  • They usually print between 10 cps to approx. 300 lpm.
    Note. All Character printers can be classified as low-speed printers.
  • The different types of low-speed printers are: -
    • Dot-matrix.
    • Daisy wheel.
    • Golf ball.
    • Thermal printers.
    • Inkjet printers.

High-speed Printers.

  • Are able to print between 300 to approx. 3,000 lines per minute.
  • High-speed printers are broadly classified into: -
    • Line printers.
    • Page printers.

Line Printers.

  • Note. Line printers have a high speed as compared to the Character printers. For example, if a line of 80 characters is to be printed, the character printer need to strike against the stationery through the inked ribbon 80 times before all the character images forming the line are passed on the stationery. A Line printer only strikes once for the whole line of 80 characters to be printed onto the stationery through the inked ribbon.
  • There are 3 types of Line printers: -
    • Drum printers.
    • Chain printers.
    • Electrostatic printers.

Advantages of using Printers.

  1. Produces a permanent output that can be maintained for future reference.
  2. The information can be conveniently distributed to reach the recipients of such information or results.
  3. The advanced models of printers with colour capabilities can produce styled prints.

Disadvantages of using Printers.

  1. Very expensive, if bought as an individual device.
  2. Some Printers are Noisy.
  3. Not possible to produce multiple copies, especially the Impact printers.
  4. Their speed of output (i.e., the printing) is slow.

Factors to consider when selecting a Printer.

The following factors are to be taken into consideration while selecting a printer.

  1. The Cost involved.
    - This will include the printer’s initial price, the costs of maintenance & the cost of consumable items, e.g. printing papers, ribbons/cartridges, etc.
  2. Volume of printing expected.
    - This will help in selecting a printer in terms of print speeds.
  3. The nature of the reports to be generated & their recipients.
    - The printing quality, such as the capability to print graphics & colour printing should be considered with respect to the needs of the recipients.
  4. The capability for the selected printer.
    - These include multiple copy production, print styles, page width, etc.
  5. Compatibility with other computers.
    - This will involve the interface with the computer system being used and/or make of particular computer.
  6. Environment in which the Printer will operate.
  7. Reliability of the Printer.
  8. Application it is required for & also the available application software packages.
  9. Stationery (type of paper) used by the printer.
  10. Documentation.

Printer driver - A program that controls how your computer and printer interact.
Tip. You might get bad work when you send graphics to a non-graphic printer or when you use a wrong driver.

Question. Explain how the factors identified in this chapter could influence the choice of printer to be used on a computer system.

Comparison between a Screen and a Printer.

Screen Printer
1. Produces a softcopy (displayed) output.
2. Output is temporary, i.e. the display gets 
lost when the power is switched off.
3. Cheaper, if bought as individual device.
4. Output is silent, since there are no
mechanically moving parts for the
display to appear on the screen.
5. Impossible to produce multiple copies.
6. Output is fast.
7. Print quality is high.
8. May cause fatigue to the user’s eyes
especially when stared at for a long duration.
9. Have different print styles, e.g., Italics
and colour displays are possible.
1. Produces a hardcopy (printed) output.
2. Output is permanent, i.e. can be maintained for future references.
3. More costly.
4. Output is noisy. Impact printers have
printing head elements that hits against the paper in order to transfer the character
images onto the stationery. Non-impact printers are considerably silent.
5. Using Impact printers, it is possible to
produce multiple copies.
6. Speed of output (printing) is comparatively slow.
7. Some printer’s quality is low while others
produce better quality prints.
8. The printed information is more convincing
to the recipients (humans).
9. Styled prints are only possible with
advanced models with the colour capabilities.

Graph Plotters.

  • These are output devices that produce graphics, such as diagrams, maps, images, statistical charts etc, on paper.
  • Plotters use pens of different types, varying thickness & different colours, in order to plot. The pens are usually under the direct or indirect influence of electronic pulses output by the computer.
  • Plotters are described/ named depending on the type of the base onto which the stationery is placed for the graphical output to be produced onto the paper.
  • The 2 commonly available Graph plotters are: -
    1.  The Drum plotter.
    2. The Flatbed plotter.

Characteristics of Graph Plotters.

  • They are large in size.
  • They use Ammonia papers.
  • They use special ink.
  • Have a wide carrying capacity.

Uses/ applications of Graph Plotters.

Graph Plotters are used: -

  • In Computer Aided Design (CAD) are mainly used for printing large architectural or engineering drawings. In this case, the computer is used to form the graphical design & the Plotter produces the output.
  • In Weather forecasting for drawing Isobars on weather maps.
  • In Statistical work for producing graphs or complicated mathematical formulas.
  • In Cartography to produce contour maps.
  • In Craft & Textile industry for drawing designs.

Advantages of Graph Plotters.

  1. Can produce information in an easily understandable form.
  2. Their presentation is quick & reliable.
  3. They produce large graphical designs of high quality, which are easy to read & use.
  4. A Plotter can be used to print even on A1 sized papers, while the largest paper size that can be used with a normal printer is A3.

Disadvantages of Graph Plotters.

  1. They require Graphic software, which is usually very expensive.
  2. Graph plotters operate at low speeds, hence are normally connected in an Off-line mode to avoid wasting the computer time.

Computer Output On Microform (COM).

  • This is the process of transforming digital data produced by the computer into human-readable form & recording it in reduced physical size into a photographic film.
  • This method of output provides photographed type of computer output stored as microscopic filmed images into the microform.
  • Microforms are photographically reduced documents on films (magnetic media).
  • There are 2 forms/ classes of the Microform: -
    1. The Microfilm, which is a film reel of 16mm.
    2. The Microfiche - a rectangular shaped sheet of film, measuring about 10 x 15 mm.
  • A typical microfiche can hold the equivalent of 300 pages of printed paper.
  • Both the Microfilm & Microfiche are small.

Differences between Microfilms and Microfiche.

Microfilm Microfiche
1. Microfilm is a photograph film.
2. Can store about 3,000 pages of A4 sized paper.
3. Displays real images in reduced form.
4. Cheap.
5. Has a long life span.
6. Requires special devices for viewing.
1. Microfiche is a normal paper.
2. Can store about 98 pages of A4 sized paper.
3. Displays sketches.
4. Expensive.
5. Has a short life span.
6. Can be viewed by naked eyes.

Advantages of Microfilms over Microfiches.

  1. Microfilms last longer than Microfiches.
  2. Microfilms display real images, making it easy to read & understand.
  3. Microfilms are cheaper compared to fiches.
  4. Microfilms require special devices for viewing while Microfiches do not.

Illustration of the COM process.

com process

  1. The computer displays the results onto the screen.
  2. The contents are then photographed onto the microform (an online operation).
    - Alternatively, the computer can write the output into a storage medium, e.g. Magnetic tape.
  3. The data on the tape is then read by transcriber machine called the Microform recorder displays them on a screen connected to the machine.
  4. The contents being displayed on the screen are then photographed by a high-speed camera using microfilm onto the microform.
    - Since the transcriber machine is not under direct influence of the computer, the operation is Off-line.
  5. The film is then developed.
  6. If necessary, duplicates are made using the Film duplicator.
    - In some systems, a separate device is needed for each of these stages. In others, the tape drive is not needed, instead the computer sends the output directly to the Microfilm recorder.
    - Also, some recorders are capable of processing the film, so a separate film developer is not needed.
    - In order to view a film, a Microfilm viewing station is used. This magnifies the images on the film so they can be easily read.
    - The station usually has a Printer connected to it to produce hardcopy, if required.

Applications of COM.

Microfilm output is conveniently suited to applications/ areas where: -

  • There is bulky storage of information.
  • The volume of output is high, say, 100,000 pages per month.
  • The data must be stored for long periods and use or update is not frequently necessary; as in case of old copies of customer’s files in banks, or back copies of newspapers. Such data is usually referred to as Archival data.
  • In Postal services, where the cost of mailing a microfiche is considerably less than mailing the equivalent bulky report.

Examples of areas where the COM is used in:

  • Libraries for books, catalogues, references, etc.
  • Government authorities - to retain/ keep Town plans, maps, statistics, etc.
  • Banks, Insurance companies, etc to store personnel or customers records.
  • National Registration Board for security purposes.
  • Registration of Motor vehicles, i.e., for Logbook and details of the vehicle.
  • Immigration department issuing of passports (originals and passports).
  • National Archives.
  • Thomas de la Rue concerned with printing of money (both original & copies).

Advantages of using the COM.

  1. Saves on stationery and space.
  2. Capable of producing many copies.
  3. A very fast form of output -usually faster than printing.
    - Using the COM, the equivalent of 30,000 40,000 lines of output can be produced per minute (which is 20 times faster than the fastest Impact Line printer).
  4. Not bulky, hence conveniently transportable.
  5. The microform contents are not easily read using naked eyes, hence guaranteeing the security of the reports.
  6. It lasts longer as compared to paper medium output.
  7. Compared to paper, the film costs are low. However, the initial cost is high, because the necessary equipment is expensive.

Disadvantages of Microforms.

  1. They are expensive.
  2. Cause eye-strain if an attempt is made to read microform contents.
  3. Requires special equipment for viewing the contents of the microform & for producing full-sized copies.
  4. The contents in a microform are not easy to update.
  5. They are less convenient.


Systems Interconnection

The Motherboard (also Called system Board or circuit Board).

  • Computers, like all electronic circuit devices are made of printed Circuit boards (electronic boards on which copper wires have been printed to form circuit paths).
  • The Motherboard is the main part (large circuit board) of your computer that every thing else plugs into.
  • It is usually a sheet of olive green or brown fiberglass with several thin gold lines on it and chips sticking off it.
  • By itself, the Motherboard is just an empty plate. It’s the hardware that sits on it that does the work. On it, we have the CPU, SIMM sockets, BIOS and slots.
  • The Motherboard provides a convenient method of inter-board connection. It is where all electronic components such as the Microprocessor, Memory chips, Interface chips, and Bus connections are assembled.
  • The motherboard also contains a no. of expansion slots in which Interface cards are slotted (plugged in).
  • The little gold lines are called Buses and act as roadways of information between all these features. The buses enable the parts to communicate and perform the functions of your computer.

Input/Output (I/O) Ports.

  • A Port is a connection or socket used to connect a device, such as a Printer, Monitor, Mouse, Scanner, etc to your computer.
  • I/O Ports are the sockets found at the back of your computer where you can connect external computer devices to the interface cards inside the computer. They allow access in & out of the computer for cables.
  • There are several types of external ports: -
    • Parallel (LPT) ports.
    • Serial (Com) ports.
    • USB ports.
    • SCSI ports.

Parallel Ports.

  • The standard PC parallel port was originally designed for sending information to Printers or Scanners. That is the reason why they are sometimes referred to as Line Printer Terminal (LPT) ports.
  • They are D-shaped with holes for 25 pins.
  • It is used mainly to connect Printers, Scanners, and sometimes external Hard drives, CD-ROM drives, Tape devices & Network adapters to your computer.
  • Parallel ports transmit data using an 8bit parallel interface & are therefore, used for devices that accept information 8 bits at a time. They transmit data byte-by-byte. They are usually faster than Serial ports.
    Note. The SCSI Port is an example of a parallel port.

Serial Ports.

  • They are sometimes referred to as Communication (COM) ports.
  • Are also D-shaped with 9 or 25 pins.
  • They are used primarily to connect devices such as serial Mice, external Modems, and sometimes
  • Printers to the System unit. They can also be used for computer-to-computer connection.
  • The Serial port has 2 data lines, one for data in & the other for data out.
  • Transmission rates of Serial ports are slower than those of Parallel ports. This is because, Serial ports transmit data bit-by-bit. Therefore, they are used for devices that accept information 1 bit at a time (or for devices that are a bit slow).

Universal Serial Bus (usb) Ports.

  • Many new PCs come with USB ports. USB ports support a wide range of desktop peripherals, e.g., Keyboards, digital Cameras, etc.
  • USB combines the best features of SCSI architecture with an advanced Plug-and-play standard.
  • It replaces the traditional Serial & Parallel ports with a single port that is extensible through the use of hubs and devices daisy-chained in a tree arrangement.
  • USB was designed to deliver a data transfer rate of up-to 12Mbits/sec to & from the PC. It also supports low-speed mode of 1.5Mbit/sec for devices like Keyboards, Mice and Joysticks.
  • USB is “user-friendly

Advantages of USB ports over Serial & Parallel ports.

  1. Devices are powered by the bus there is no need for external power adapters. USB allows unpowered devices to draw up to 500 mA over the connector cable.
  2. Can support a max. of 127 daisy-chained devices, because of its high bit addressing system. 

SCSI (Small Computer Systems Interface) PORTS

  • Pronounced as Scuzzy.
  • SCSI is a device interface used by PCs, Apple Macintosh computers and many UNIX systems.
  • Small Computer System Interface (SCSI) card is used for attaching to peripheral devices that require high speed data transfers between the device and memory.
  • The SCSI cards provide parallel high-speed data transfer in the range of 10 MB/s to the memory.
  • It connects peripherals to your computer via standard hardware interface, which uses standard SCSI commands.

Components Assembly.

  • The basic Microcomputer system consists of the Motherboard, the Power Supply unit, Hard disk & Floppy disk drives, I/O interface cards, Disk controller card, Video card, optional CD-ROM drive, Sound and Network interface cards.
  • All these components are housed in a cabinet (or Chassis). The cabinet has rear connectors for peripheral devices through the motherboard or interface cards.
  • The Interface cards are usually plugged into the microcomputer’s card slots with power-supply voltages and bus signals distributed to the card slots.
  • Cables then go from connectors on the interface cards to the peripheral devices.

components assembly



Computer Software.

  • Software refers to the various programs & data used in a computer system that enable it perform a no. of specific functions.
  • Software instructs the computer on what to do and how to do it.
  • All programs (software) are written using programming languages.
  • Programmers usually write programs in Source Language (a language that is like broken English). The Source language is then converted into Machine language; the language that the computer can understand.
  • Machine language is usually in form of bits (series of 0s & 1s).

Software Flexibility.

  • The Software used on a given computer is said to be flexible, i.e. it is relatively easy to change.
  • For example, in a home computer used for playing games, instead of buying a new machine each time a new game is needed, you only need to ‘load’ a new program into the machine. Again, it is relatively easy to change between games at will.

Classification of Computer Software.

  • Computer software can be broadly classified/ divided into 2 categories: -
    1. System Software (programs).
    2. Application software (programs).
  • Note. Programming languages can also be considered part of software, because they form the basis of grammar on which the program’s development is based.
  • The following figure illustrates the computer software family tree.

classification of software

Systems Software.

  • This is a set of programs, which is developed & installed in a computer system for the purpose of developing other programs, and to enhance the functional capabilities of the computer system.
  • System programs control the operation of the various hardware parts & make them available to the user. They also enable users make efficient use of the computing facilities in order to solve their problems.
  • System programs manage the computer resources such as Printers, Memory, disks, etc, automate its operations & make easier the writing, testing and debugging of users’ programs.
  • They also control the various application programs that we use to achieve a particular kind of work.

    Notes.
    • System software are developed & installed by the manufacturer of the computer hardware. This is because to write them, a programmer needs in-depth knowledge of the hardware details of the specific computer.
    • Some of the system software are supposed to put initial ‘life’ into the computer hardware and are therefore, held permanently in the ROM. Program routines that are permanently maintained in the computer’s memory are called Resident software/ routines.
    • System programs dictate how the programs relate to the hardware, and are therefore said to be Hardware-oriented.
  • System programs consist of Operating Systems, Language translators (Assemblers, Compilers), System utilities, and Device drivers.
  • System software is further sub-classified as:
    1. Operating system.
    2. System utilities.

Examples Of System Programs.

  1. FIRMWARE (or Microprogram).
    - It refers to a series of special program instructions.
    - The Microprogram is held in the Control Unit (CU), and is used to interpret the external Instruction set of a computer.
    - The Instruction set is the list of instructions available to the programmer that can be used to give direct orders to the computer.
    - Firmware is fixed into the ROM, and cannot be changed.
    - Firmware is usually a combination of hardware and software. It deals with very low-level machine operations, such as moving data, making comparison, etc, and thus acts as an essential substitute for additional hardware.
  2. OPERATING SYSTEMS.
    - An Operating System is a set of programs designed to ensure the smooth running of the computer system.
    - They are developed to manage all parts of the basic computer hardware & provide a more hospitable interface to users and their programs.
    - It controls the way the way the software uses the hardware. This control ensures that the computer system operates in a systematic, reliable & efficient manner as intended by the user.
    - OS are supplied by the computer manufacturer. They are designed to reduce the amount of time that the computer is idle, and also the amount of programming required to use a computer.
  3. UTILITY SOFTWARE (Service programs).
    - Modern OS does a lot more than manage the hardware efficiently. It normally provides the user with facilities that make the job of developing programs or doing something useful on the computer much easier.
    - A Utility program is a program, which performs a generally useful task.
    - Utility programs are used by end-users to perform many of the routine functions & operations such as, sorting, merging, program debugging, manage computer files, diagnose and repair computer problems that occur, etc. They are normally supplied the manufacturers to enable the computer to run more smoothly & efficiently.
    - Most OS have many of the Utility programs needed to assist with the upkeep of the computer. For example, DOS 6.x includes utilities for managing memory, protecting a system of viruses, backing up files, restoring accidentally deleted files, etc.
    - Some of the common Utility programs are those concerned with: -
    1. Searching.
      - They help to search for a file from one or more specified records. For example, in a Sales record, the Search facility assists in finding the salesperson with the highest sales.
    2. Moving data from one medium to another.
      For example, from tape to disk & vice versa, or from a floppy disk to hard disk.
    3. Spell-checking of words.
      - After a document is typed, the words in the document are checked against those in a ‘custom dictionary’ in secondary storage. If any word used is not found in the dictionary, a warning is given indicating a possible spelling error.
    4. Formatting programs.
      - Before a floppy disk can be used, it must be ‘initialized’ or formatted. This means that, the system must put certain information on the disk, which helps with the storing and retrieving user’s programs & data at a later time.
      - Therefore, a computer system that uses disks would have a utility program for initializing or formatting these disks.
    5. Debugging (removing program errors).
      - The programming process usually includes debugging (removing errors from) a program. Statements of the program are studied to determine the cause of an error.
      - Again, useful information can be obtained by studying the contents of memory at the time the program failed.

    Examples of the common Service programs.
    1. Text Editors.
    2. Language Translators.
    3. Diagnostic Tools/ Programs.
    4. Sort utility.
    5. Merge utility.
    6. Copy utility.
    7. Core/ Dump utility.
    8. Linker.
    9. Loader.
    10. Library Program.
    11. Database management system (DBMS) – a utility program that manages data contents.

    Text Editor.
    • This is a utility program that enables/ allows users to create files in which they can store any textual information they desire using the computer.
    • Once the files are created, the Text editor provides facilities which allow the user modify (make changes to) the files; such as adding, deleting, or changing information in the file.
    • Data can be copied from one file to another. When a file is no longer needed, it can be deleted from the system.
    • The operations of the Text editor are controlled by an interactive OS that provides a ‘dialogue’ between the user and the Operating system.
    • The Text editors are used to create, e.g. program statements through the Keyboard connected to the computer. Editing can then be carried out using the Edit keys on the Keyboard or by using a sequence of commands.
    • There are 3 major classes of Text editors:
      1. Character text editors – deals with 1 character at a time.
      2. Line text editors – deals with a whole line at a time.
      3. Page text editors - deals with a whole screen full of text at a time.
    • Note. The Text Editor is probably the most often used utility program of an OS.

    Sort utility.
    • The Sort utility is used to arrange the records within a file according to some predetermined sequence. The arrangement can either be in Ascending or Descending order of the alphabets or numerals.
    • For example, a user may wish to sort data into some desired sequence, such as; sort a student file into ascending order by name or into descending order by average grade or sort a mailing list by postal code, etc.

    Merge utility.
    • Merging is the process by which the records in two or more sorted files are brought together into one larger file in such a way that, the resulting file is also sorted.
    • The Merge utility is used to influence the combining of the contents of 2 or more input files to produce one output file.

    Copy utility.
    • It is usually advisable to maintain duplicate copies of the operational files so that in case something goes wrong with the original files, then their contents can be recreated from the duplicate/ backup copy or copies.
    • The duplication process, i.e. copying the contents of one file to another is done through the influence of the Copy utility. The copying can be from one media to a different media or from one media to another media of the same make, e.g. from diskette to hard disk or from a diskette to another diskette.

    Dump utility.
    • The term Dumping is used to describe the copying of the contents of the main memory.
    • The Dump utility is therefore, used to transfer (copy) the contents of the computer’s internal memory into a storage media, e.g. the disk or through the Printer (to get a Hard copy output).
    • The result of dumping is that the main memory ‘image’ is reflected by the stored or the printed contents.

    Language Translator.
    • Programs written in high-level languages have to be translated into binary code (Machine language), before the computer can run these programs.
    • Translator is a utility program written & supplied by the computer manufacturers, used to convert the Source Codes (the program statements written in any of the computer programming languages) to Object Codes (their computer language equivalents).
    • Each language needs its own translator. Most OS provide users with Compilers or Interpreters for the common high-level languages. In addition, an Assembler is usually available for those wishing to write programs in the Assembly language of the particular machine.
    • Note. These translators are not part of the OS, but they are designed to be used under the operating system & are accessible to it.

    Linker.
    • Computer programs are usually developed in Modules or Subroutines (i.e. program segments meant to carry out the specific relevant tasks).
    • During the program translation into their machine code, these modules are translated separately into their object code equivalents.
    • The Linker is a utility software that accepts the separately translated program modules as its input and logically combines them into one logical module, known as the Load Module that has got all the required bits & pieces for the translated program to be obeyed by the computer hardware.

    Loader.
    •  The Loader is a utility program that transfers the load module (i.e. the linker output) into the computer memory, ready for it to be executed by the computer hardware.
    • The transfer process is from the backing store, e.g. magnetic disk into the computer’s main memory. This is because some systems generate object codes for the program, but instead of being obeyed straight away, they store them into the media.

    Diagnostic Tools (Programs).

    • Diagnostic tools/programs usually come with the translators and are used to detect & correct system faults both hardware and software.
    • They provide facilities which help users to debug (remove errors from) their programs more easily.
      E.g., Dr.Watson is a diagnostic tool from Microsoft that takes a snapshot/ photograph of your system whenever a system fault occurs. It intercepts software faults, identifies the software that faulted, and offers a detailed description of the cause & how to repair the fault.
    • Other diagnostic tools for detecting hardware faults are, Norton Utilities, PC Tools, QAPlusetc.
  4. PROGRAMMING LANGUAGES.
    - A computer usually ‘works’ by executing a series of instructions called the Program. A Computer Program is simply a sequence of numeric codes (‘0’s & ‘1’s). Each of these codes can be converted directly by the hardware into simple instructions.
    - The set of instructions that the computer can recognize is referred to as the Instruction Set.
    - A Computer program can be written in a variety of programming languages.
    - A Programming language is a language used in writing a computer program. The languages must be understood by the computer for it to execute.
    - The languages are broadly classified into 5 categories: -
    1. Machine (computer) language.
    2. Low-level programming language (also referred to as Assembly language).
    3. High-level programming languages.
    4. 4th Generation languages (4GL’s).
    5. 5th Generation languages (5 GL’s).

    1. Machine language (1st Generation Computer language).
    - This is the language that is readily understood by the computer.
    - Machine language uses machine codes (binary digits) that consist of 0’s & 1’s.

    2. Low-level languages/ Assembly language (2ND Generation languages).
    - Assembly language is very close to the vocabulary of the machine language.
    - It uses many English-like acronyms (Mnemonic codes or labels). Words like ADD, SUM could be used in programs, and a program called an Assembler translates these words into Machine language.
    - It was developed (in early 1950s) to speed up programming.
    - The Assembly language instructions are Symbolic representations of the machine code (computer language) instructions.
    - Comments can be incorporated into the program statements to make them easier to be understood by the human programmers.

    3. High-level languages (3RD Generation languages).
    - These are languages developed to solve the problems encountered in low-level programming languages.
    - The grammar of High-level languages is very close to the human being’s natural languages vocabulary, hence easy for the human beings to understand and use.
    - They allow a problem solution to be specified in a human & problem- oriented manner.
    - The programs are able to run in any family of computers provided the relevant translator is installed.
    - Programs written in high-level languages are shorter than their low-level equivalents, since one statement translates into several machine code instructions.

    Examples.
    • COBOL (COmmon Business Oriented Language).
    • FORTRAN (FORmula TRANslation).
    • BASIC (Beginners All-purpose Symbolic Instruction Code).
    • PASCAL.
    • C.
    • C++ (Object C).
    • LISP (LISt Processing).
    • LOGO.
    • COROL.
    • RPG (Report Program Generator).
    • SNOBOL (String Oriented Symbolic Language).

Application Software.

  • Application programs are written to solve specific problems (or to handle the needs) of the enduser in particular areas.
  • They interface between the user & system programs to allow the user to perform specific tasks. 
  • Application software helps to solve the problems of the computer user, and are therefore said to be user-oriented.
  • They are designed specifically to carry out particular tasks. For example, they can be used to type & create professional documents such as letters, solve mathematical equations, draw pictures, etc.

    Notes.
    • Application programs can be written by the user, programmers employed by the user, or by a Software house (a company specializing in writing software).
    • Application programs can be written with very little knowledge of the hardware details of a specific computer, and can run on several different computers with little or no modification.
  • Application software falls into 2 main categories/groups: -
    1. General-purpose packages (Application packages).
    2. Special-purpose applications (User programs).

General-purpose packages (Application packages).

  • They are usually pre-written programs made for non-specialists, in the home or business, and may be used for a wide variety of purposes.
  • They are off-shelf programs that are developed & supplied by manufacturers, Bureaux & software houses at a price.
  • They provide a general set of facilities that are used in dealing with similar types of tasks, which arise in a wide variety of different application problems.
  • The range, quality and variety of the packages are continuously changing.

    Examples of Application packages are: -
    • Word processors * Spreadsheets.
    • Databases * Graphic packages, etc.
  • Package - a set of fully described & related programs stored together to perform a specific task.
  • They are developed to solve particular problems in one or more organizations with little or no alterations.

Advantages of Application packages as compared to other forms of applications.

  1. Packages save a lot time & programming effort, because the company buys the software when it is ready-made.
  2. Are relatively cheap to the user. These programs are usually sold in large numbers. Again, the cost of developing the programs is effectively shared between the purchases.
  3. They are appropriate for a large variety of applications.
  4. Most packages are menu-driven, i.e., the user is provided with a set of options displayed on the screen; hence, they are easy to learn & use, making them suitable for people with little or no computing knowledge.
  5. Packages are extensively/thoroughly tested & debugged (has all errors corrected), i.e. if it is a popular package, it is usually tried & approved by a large no. of people. The testing is done by a pool of professional programmers and analysts.
  6. Are usually provided with extensive documentation to help the user.
  7. Relatively quick results are obtained.
  8. The packages are generally portable. In addition, there is usually a maintenance agreement between the supplier & the buyer.
  9. Application packages can be rented, especially by users who might require to use them only periodically, hence cutting on costs, e.g. maintenance.

Disadvantages (drawbacks) of Application packages.

  1. The package is produced to meet general needs (a wide variety of user’s needs) therefore, may not be ideal for a particular customer/ company.
  2. The purchaser has no direct control over the package, because he/she is not involved in developing it.
  3. Packages cannot be modified.
     - The user may not be free to correct any routines/ functions of the package, because there is always a maintenance guarantee & the application of the developer’s copyright acts.
  4. A package may include extra facilities, which are not required by an individual user or company.
  5. Sometimes, the package will allow only a clumsy solution to the task at hand.
  6. In the case of Spreadsheet or Database, the user must still develop the application, which requires a thorough knowledge of the capabilities of the package, which are usually quite extensive.
  7. The user must still provide documentation for the particular application that he/she has created.
  8. It is quite easy to forget the commands to use the package, especially if it is not used frequently.

Special-purpose applications (User-developed/ in-house programs).

  • They are written to meet the specific needs of an organization.
  • They are usually customized (modified/ tailored) programs written by the user or a Software house under contract, to perform a specific job.
  • They are developed by users to solve only the specific processing tasks in one organization, and may not suit the needs of other organizations, hence the name In-house or Tailor-made programs.
  • They are designed for a particular identifiable group of users such as Estate agents, farmers, Hoteliers, etc.
  • They are usually aimed at providing all the facilities required for particular class of application problem such as Payroll / Stock control.
  • Since the programs are occupation- specific; they sell fewer & tend to be more expensive.

Advantages of Special-purpose applications.

  1. The user gets a well tried & tested program, which he/she is able to use with confidence.
  2. The user is able to quickly implement the results obtained from the use of the package.

Disadvantages of Special-purpose applications.

  1. Purchaser has direct control over the package, as he is involved in its production.
  2. Are very expensive.

Factors to consider when buying an Application package.

- The following are some of the factors that a buyer who is intending to acquire an Application package should consider: -

  1. Cost of the package in relation to the expected benefits against the cost of developing inhouse programs.
  2. Compatibility: - (fitting) of the package with/within the existing computer resources, e.g., hardware, software, etc.
  3. Whether there is maintenance support from the suppliers.
  4. Whether there is accompanying documentation (the descriptions), which helps in using, maintaining & installing the package.
  5. The portability of the package, i.e. whether the package can be used on different families of computers.
  6. A good package is that which is easy to learn & use. This helps to determine the duration of training that might be involved & the subsequent cost of training.
  7. Before buying a particular package, its current users should be interviewed to find out whether the package is successful and famous in the market.

Examples of Application Packages.

Word Processors.

  • A Word processor is a computer system with a special piece of software used for the production of documents.
  • Word processors can be used to prepare & produce letters, documents, books, articles, mailing lists and any material that involves text.

    Common examples of Word processors: -
    • Microsoft Word.
    • WordPerfect.
    • Lotus Word Pro.
    • WordStar.
    •  Wang writer.
  • Depending on the task & the type of output required, either Text Editors or Word processors can be used.

Text editors.

  • A Text editor is the simplest Word processor. Text editors are mainly used to write small notes, memos and programs.
  • A Text editor is used to type text without any special formatting; however, the document can be saved, retrieved and modified at will.
  • The 2 types of Text Editors.
    1. Line Editors - allow users to work with one line of text at a time.
      - An example of a line editor is the DOS COPY CON.
    2. Screen Editors. These are full screen editors that allow users to work with large files of up to 64 KB in size.
      - They use Special keys that can be used to Cut, Copy, Paste & Delete blocks of text.
      - They also have a Search & Replace facility, which can be used to easily search for a specific text and replace it with something else.

Spreadshhets.

  • Spreadsheets are application packages used for manipulation of figures. A spreadsheet application lets the user enter numerical data.
  • A Spreadsheet usually consists of a series of rows & columns in which data entries can be made.
  • The figures or text are inserted into the Cells. A cell is referred to by the column letter and row number (e.g., A1 refers to the first cell).
  • The package is suited for Accounts oriented work since it has in-built formulas that enable users to perform complex calculations.
    • Spreadsheets provide an easy & streamlined means for financial planning.
      - Using Spreadsheets, Sales & purchases can be recorded, Invoices produced and statements compiled.
      - The management can keep track of the current state of payments from customers in relation to goods dispatched.
    • Researchers can compile and analyse their results.
    • Teachers can compile their students’ marks and produce results.
    • Clerks and secretaries can easily create tables of figures and manipulate them quickly as required.

Examples of Spreadsheet packages in the market today: -

  • Microsoft Excel.
  • Lotus 1-2-3.
  • Quattro Pro.

Database management systems (DBMS).

  • A Database is a tool that is used to store large volumes of data in a compact & well-organized manner.
  • A Database application can be used to store, track and manage files/ records containing related information.
  • They generally allow users to create database files, enter data, organize that data in various ways, and create reports.
  • You can create a database for customer’s records, financial records, library records, personal records, etc. The database will help you sort through your records & compile lists based on any criteria you like to establish.

    Examples of Database management system programs;
    • Microsoft Access.
    • FoxPro.
    • Dbase.
    • Paradox.

Graphics programs.

  • Graphics applications are used to create artwork that can be printed or incorporated into other applications such as, Desktop publishing packages and Word processing programs.
  • They can be used to create simple line drawings, charts or presentations.
  • There are different kinds of Graphics programs, all designed to help the user create drawings and illustrations that can be used for different purposes.
  • Some of the basic categories of Graphics programs include: -
    1. Clip Art Programs that come with pre-drawn artwork that you can simply copy into any document.
    2. Draw & Paint programs that have tools you need to create your own artwork.
    3. Computer Aided Design (CAD) Programs, which are sophisticated versions of draw and paint packages that you use to create detailed images, such as schematics and Blueprints. CAD programs often include 3-D imaging.
    4. Presentation Graphics software.
      - Presentation Graphics software is mainly used to create & design outputs (usually Slides) for presentations. They can be used, for instance, by an advertising agency for creating advertisements for Television. These could be sales presentations, management reports and product demonstrations.

      Features of a Presentation program.
      • You can create slides, which can be used in a slide show.
      • You can incorporate ClipArt pictures in a slide (ClipArt is a collection of ready-made graphics you can add to your presentation).
      • Presentation Graphics software allows the user to draw charts, graphs & other pictorial data using in-built objects such as, rectangles, ellipses, lines, etc. The user can also add text, and scanned images/ photographs. All the objects can be transformed by sizing, rotating & flipping.
      • The pictures can be decorated using different colours & shadings, making the presentation look great.

      - To create a Slide show, all the pages/ slides required should be created first. The user can then arrange them in the desired sequence to form a complete presentation (or Slide show).
      - Special effects can be added to each slide as it is activated & deactivated during the presentation.

      Examples of Presentation Graphics packages:
      • Microsoft PowerPoint.
      • Corel Draw.
      • Adobe Photoshop.
      • Harvard Graphics.
      • Lotus Freelance Graphics.
      • Adobe Illustrator.

Desktop publishers (dtp)

  • Desktop publishing is used to create documents that look like typeset professional publications.
  • Usually, Desktop publishing programs combine data from other applications such as, text from Word processors and artwork from a Graphics package.
  • DTP is used to handle documents involving printed text, diagrams and images.
  • DTP programs can be used to create Newsletters, Reports, Books, & any other documents that may require page layout.

Common features of a Desktop publishing package.

  • Page formatting features that are used to set Margins, Headers, Footers, Columns, and other page design features.
  • Templates that save a page layout for use in other documents.
  • Text editing features that enable the user to make changes to text, set fonts & styles, move and position text on a page.
  • Built-in fonts that give the user printed materials a unique and original appearance.

Examples of Desktop publishing packages: -

  • Adobe PageMaker.
  • FrameMaker.
  • Microsoft Publisher.

Computer Aided Design (cad).

  • CAD is mainly used in Engineering design & Architectural drawings. It is used by engineers, scientists, architects to speed up their design process. CAD is widely used in Computer simulation.

Simulation

  • Computer simulation involves trying to predict what will happen in a real-life situation from a model of that situation.
  • For example, a CAD program may be used by;
    1. An Architect to ‘try out’ various designs of a building.
    2. CAD is widely used in the design of electronic circuits, ships, roads & cars.
    3. When designing a bridge, an Engineer would like to know the effects of various loading conditions on the bridge without actually having to build the bridge.
    4. An Aeronautical engineer to determine how a different tail design will affect the performance of an aircraft.
      - The Aircraft designer would like to know the effect on lift, say, of changing the shape of the wings or the tail without having to build an aircraft with these changes.
      - A computer is a useful tool in providing answers to these questions.
    5. It is used in computers in the manufacture of industrial products, in what is referred to as Computer Aided Manufacturer (CAM).
    6. CAD programs are also used to simulate the timing of traffic lights or a nuclear attack for testing national defenses.
  • CAD makes it easy to make drawings & modify them at will, allowing the designer to focus more on the actual design, the specifications and functionality of the final product.
    Note. The results obtained depend heavily on the models used. The more accurate the model, the more reliable the results will be.

    Examples of CAD packages: -
    • AutoCAD.
    • ArchCAD.
    • Architectural Desktop.
    • Planix Home Designer 3D Deluxe.
    • SoftPlan.
    • 3dsMacs.
    • Draffics.

Multimedia Programs.

  • Multimedia refers to a combination of text, graphics, sound, animation and video.
  • Multimedia is essential in many software applications. For example, Word processing and Desktop Publishing documents can be enhanced with graphics, photos and charts. Sound and animation can be added to make presentations exciting.
  • Multimedia subjects include; children’s learning, History, Geography, hobbies, sports and games.
  • Multimedia software comes on a Compact Disk (CD-ROM), because they require a large storage space.
  • The minimum requirements for Multimedia software as set by the Multimedia Personal Computer (MPC) Marketing Council include: -
    • CD-ROM Drive.
    • Hard disk drive with sufficient storage capacity.
    • A 486, or Pentium processor.
    • At least 4, 8, or 16 MB of RAM memory.
    • A 256 colour or a better Video Adapter.
    • A Sound card with Speakers or headphones. A Microphone (is optional) if you want to record your own sounds.

Examples of Multimedia packages: -

  • Animation Master 99.
  • 3D Studio Max.
  • Extreme 3D.
  • Morpher.

Communication Software.

  • Communication software is used to exchange information, messages and ideas with people around the world who have PCs equipped with Modems & communications software.
  • To use a communications package, you need a Modem & a Telephone line.
  • The basic purpose of a communication program is to control the way the computer transmits & receives data.

    Examples of communications packages: -
    • WinFax Pro.
    • Zoc.
    • ProComm Plus.
    • HyperAccess.

Internet Software.

E-Mail (Electronic mail).

  • E-mail is a quick, convenient, efficient & cheap way of communicating with both individuals and groups.
  • E-mail is much faster than regular mail. With e-mail, the message can reach the recipient in hrs, minutes or even seconds.
  • E-mail is also convenient since you can send your messages when it is convenient for you and your recipients respond at their convenient times.

    Examples of e-mail packages: -
    • Microsoft Exchange.
    • Outlook Express.
    • Netscape Mail/Messenger.
  • Note. All e-mail software must have the capability of writing messages, sending & receiving e-mail.

Browsers.

  • Browsers are software that enable the user to surf (log in / use) the World Wide Web (www). The WWW provides users on computer networks with a consistent means to access a variety of media in a simplified fashion.
  • The most commonly used browsers are: -
    • Internet Explorer.
    • Netscape.
    • Cello Internet browser.
    • NCSA Habanero.
    • Chrome
    • Mozilla Firefox

Money Management Software.

  • Money management programs are designed specifically for working with money.
  • They have features that help people balance their Cheque books, manage a budget, keep track of bills & payments, and control monies being spent.
  • Money management software falls into 2 categories: -
    1. Personal Finance programs.
      - They help people set up personal budgets, plan retirements & pay bills electronically.
      Examples;
      • Quicken.
      • Microsoft Money.
    2. Accounting programs.
      - Used by businesses to help them manage their financial affairs. They help to organize the accounting & spending plans of small businesses.
      - These programs keep track of expenditures, payrolls, inventory and operating income. The programs usually include a budget system, cheque register, report system and savings planner.
      Examples;
      • Point-of- sale. 
      • Acc Pac. 
      • DAC Easy.
      • Peachtree Accounting.
      • Systematics.
      • Pegasus.

Personal Organisers.

  • Personal Organizers act as electronic Secretaries or Assistants. They are used to store addresses & phone numbers, schedule meetings and appointments.

    Examples of Personal Organisers are: -
    • Organiser.
    • Goldmine.
    • Ecco Pro.
    • Day-Timer Organiser.
    • Day Runner Planner.
    • Sidekick Deluxe.
    • Sharkware Pro.
    • Outlook.

Payroll programs - used to generate the payroll of many businesses.

Stock-control Programs - used by businesses to manage their stock efficiently.

Educational Programs - used in schools for teaching various subjects.

Administration Programs - used by organizations for maintaining records of employees, customers, clients, students, creditors, members, etc. 

Library Control Programs - used by libraries for maintaining records of books & borrowers in order to provide faster & more efficient service.

Software Suites.

  • A Software Suite is a group of different compatible applications sold by one software company.
  • The programs are each individual applications, but they usually work in a similar manner, and have some common features, such as menu commands, buttons, or keystrokes.
  • Although each of the programs in a suite can be purchased separately, they cost less when purchased as a bundle.
  • Typically, a suite includes a Word processor, a Spreadsheet, a Database, Presentation graphics applications, Personal Information Managers, and E-mail applications.
  • The applications are integrated with one another, making it easy to use them together and to transfer data from one into the others.

    Examples of Software Suites are: -
    • Microsoft Office.
    • LotusSmart Suite.
    • WordPerfect Suite.
    • Microsoft Works.
    • ClarisWorks.

Software as a Product

  • Software is normally purchased directly or indirectly from either a computer manufacturer or a ‘Software house’.
  • A Software house is a company that specializes in producing software and related services.
  • When software is purchased for use on a particular computer, the purchaser obtains a copy of the program plus a no. of other items of documentation.
  • Software may therefore refer to the various programs used in a computer system together with their associated documentation.
  • The purchaser of software usually pays for some or all of the following: -
    1. LICENCE.
      - The purchaser pays a Licence Fee, which gives him/her the right to use the software on a particular computer or a specified no. of computers on a particular site.
      - Alternatively, a Site Licence may be paid, which entitles the purchaser to use the software on any computer at a particular space. Sometimes, the licence may specify the no. of users that may use the software at any one time, and in case of a Single-user licence, the users’ name must be registered.
      - Note. Using software in breach of licence agreements is a serious offence for which the user may be sued for damages or subjected to criminal prosecution.
    2. INSTALLATION GUIDE.
      - The guide provides information about what hardware is needed to enable the programs to run satisfactorily.
      - It tries to describe the procedures to be followed in order to set up the software, so that it can be used satisfactorily & efficiently on a particular kind of computer.
    3. INSTALLATION OF THE SOFTWARE.
      - If the purchaser is not an expert in setting up the software, he pays an additional fee to have the software installed.
    4. MAINTENANCE UPDATES.
      - Sometimes, faults called Bugs may light up sometime after the software has been delivered and put to use.
      - A good supplier will make every effort to correct bugs as and/or when they are discovered & will provide a new corrected version of the program containing the necessary “Bug fixes”.
      - The correction of bugs (i.e. maintenance) is often combined with enhancements to the software to make it better in some way. Enhancements normally involve increased “functionality”, i.e. making it work faster.
      - Licensed purchasers may get some of these changes provided free of charge, perhaps during the 1st year of use. Subsequently, the purchaser may be required to pay an annual fee for maintenance and updates.
    5. USER GUIDES.
      - A User Guide is usually a manual provided for the end-user to enable him/her to learn how to use the software. Such guides usually use suitable examples to take the user through the stages of carrying out various tasks with the software.
    6. A REFERENCE MANUAL.
      - A reference manual is normally intended to be used by a user who already knows how to use the software, but who needs to be reminded about a particular point or who wants to obtain more detailed information about a particular reference.
      - Reference manuals normally have topics organized in alphabetical order.
    7. A QUICK REFERENCE GUIDE.
      - This may be a single sheet or card, which the user may keep for help with common tasks carried out with the software.
    8. TRAINING.
      - The software supplier may provide training courses on how to use the software.
      - Sometimes, some initial training is provided free as part of initial purchase.
    9. MEMBERSHIP OF A USER GROUP.
      - A User group is a club for individuals or organizations who use a particular hardware or software product. The club is often run and partly sponsored by the supplier.
      - Members of user groups receive Newsletters, which enable them to find out more about the product & how to use it.


Selecting a Computer System.

  • When planning to acquire computer equipments, the individual or organization should carefully weigh the merits and demerits of the methods used to finance the equipment
  • The requirements analysis for selecting a computer system should cover the following:
    1. Identify all requirements of the user.
    2. Evaluate hardware requirements that will meet the user’s needs.
    3. Evaluate software requirements that will meet the user’s needs.

Factors to consider when selecting a computer system.

The various factors to be considered in selecting a computer system are categorized as follows;

  1. Economic factors.
    - Cost comparisons.
    - Acquisition methods.
    - Return on investment.
  2. Hardware factors.
    - Hardware performance, reliability, capacity, and price.
    - Firmness of delivery date.
    - Accessibility of back-up facilities.
    - Presence or absence of modularity.
    - Effective life of the proposed hardware.
    - Compatibility with existing systems..
  3. Software factors.
    - Software performance and price.
    - Firmness of delivery date on the proposed software.
    - Availability of useful and well-documented packaged programs.
    - Ease of use and modification.
  4.  Service factors.
    - Maintenance terms and quality.
    - Training facilities offered and the quality of training provided.
    - Programming and conversion assistance offered.
    - Facilities provided by the manufacturer for checking new programs.
  5.  Reputation of a manufacturer.
    - Financial stability.
    - Clean record of keeping promises.

Hardware Factors.

Some factors considered when selecting a computer hardware are:

  1. Processor Speed.
    - Every computer has a clock that drives its operation. The Processor speed is the speed at which the system Clock synchronizes the operations of the CPU & can be measured in Hertz or Megahertz (1MHz = 1 million cycles per second).
    - The processing power of a computer depends on its Processor speed & the amount of data it can handle at the same time.
  2. Memory capacity (amount of Main memory RAM).
    - All computers have some amount of Random Access Memory (RAM). RAM is a section of the Main memory, which is used for holding data & instructions required immediately by CPU to perform a task.
  3. Warranty (Service contract/ assurance/ guarantee).
    - A Warranty is an agreement between the buyer and the seller that spells out terms and conditions of, after selling a product in case of failure or malfunction.
    - A Warranty is usually the duration in which your computer is supposed to work without any problem.
    - A good warranty should cover the following points:
    • Scope of cover, such as 6 months, 1 year, etc.
    • Callout response and liability agreement. .
    • Preventive maintenance.
  4. Cost of the system.
    - The cost of a computer system depends on:
    1. Its Processing capability.
    2. Its Size.
      - The cost of a computer is directly related to the size. Portable computers are more expensive than their desktop equivalents, because of the superior technology involved to manufacture smaller components without losing performance abilities.
    3. Whether it is branded or a clone. Branded computers are more expensive that their equivalent clones. This is because of their reliability and good after sale services.
  5. Upgradeability of the computer.
    - The type of the computer purchased should be upgradeable, i.e., it should allow upgrading of the Processor & the Hard disk to make it suit your needs. The RAM memory can also be upgraded/ increased by simply adding new memory modules into the memory slots on your Motherboard.
  6. Compatibility of the system.
    - The hardware facilities of the computer should relate well with the different kind of devices available. It must also support Plug-and-Play facilities.
    - This ensures that the computer system operates in a systematic, reliable, & efficient manner as required by the user.
  7. Portability.
    - The size of the computer should be small so as to enhance portability. In other words, it should be sufficiently light & hence easily transportable.
  8.  User needs.
    - The computer hardware selected should be able to accommodate the user programs as well as any other device which might be added; both hardware and software.
    - User needs also determine the type of data that will be processed. Therefore, the type of hardware chosen should be the most appropriate to satisfy the needs. For example, in a
    - Supermarket, a special device called a Point of Sale (POS) Terminal is most suitable to record transactions.
  9. Popularity of the computer manufacturer.
    - The computer must be from a well-known manufacturer. This can only be detected by use of the brand names such as Compaq, Dell, IBM, and Hp.
  10.  Availability of hardware spare parts.
    - The computer spare parts, i.e., Input and output devices, should be readily available.
  11. Monitor.
    Depending on preference, your choice for a monitor may depend on Size, resolution, and the technology used to make it.
    - Currently, Flat panel displays have become a new market standard quickly replacing the Cathode Ray Tube (CRT).
  12. Multimedia capability.
    - Multimedia is the combination of video, audio, text, and images to provide an interactive, creative, and effective way of producing and communicating information.
    - A multimedia system should have Speakers, CD/DVD drive, Sound card, and a SVGA monitor. It should also have software that supports multimedia capability.

Software Factors.

The following factors should be considered when selecting software:

  1. Authenticity of the software.
    - The term Authenticity refers to genuineness, validity or legitimacy of an item.
    - When acquiring software from the vendor, make sure it is the original copy that is accompanied by the license and certificate of authenticity of the developer.
    - You should only use software of the major Software houses.
  2. Documentation of the programs.
    - Documentation refers to the manuals prepared by the developer having details on how to install, use and maintain the software.
    - These include; Installation guide, Maintenance guide, User guide, a Reference manual, etc.
    - This documentation enables the user to work with the software with minimum guidance.
  3. User needs (requirements) of the software.
    - The needs of the user determine the type of operating system and application programs that should be purchased..
  4. Reliability and security.
    People are more comfortable with software that offers good security to confidential and private information.
  5. User friendliness of the software.
    - The software purchased is expected to be “User-friendly”. User-friendliness is a measure of how easily the user can be able to operate the computer.

    Features/characteristics of User-friendly software.
    • It should be easy to learn & use and also suit people with little or no computing knowledge.
    • The programs should enable the end-user to perform many of the routine functions & operations such as, manage computer files, diagnose & repair computer problems that enable the computer to run more smoothly & efficiently.
    • The software should be self-contained, so that the user is not forced into accessing manuals.
    • The amount of effort & the information required for the user to get the software complete required tasks should be minimal.
    • The user should be made to feel in control of what is going on.
    • The software should behave in a logical & consistent manner, enabling the user to reason about what is going on and apply what has been learned.
  6. Cost of the Software.
    - The software purchased should be relatively cheap, and should be able to meet one’s needs.
    Note. One cannot just buy a program because it is cheap. There are many other factors that may force a person to buy far much more expensive software even with cheaper alternatives available.
    - In case the off-the-shelf software does not fit the needs of the users, it would be advisable to develop in-house software, even though they may be a bit more expensive.
  7. Compatibility and System requirements of the software.
    - Software compatibility refers to the ability of the computer to run depending on the system setup (configuration).
    - Different programs will be loaded to different types of hardware. For example, some software may only run on a computer that has 32MB or RAM and above. Any computer, whose configuration is lower than this, is said to be incompatible.
    - Therefore, the programs selected should relate (fit) well with/within the existing computer resources, e.g., hardware facilities and ensure that the computer system operates in a systematic, reliable & efficient manner as intended by the user.
    - Some software are not compatible (well suited), e.g. Apple Programs. Otherwise, it is important that one reads the installation guide and system requirements that comes with the software in order to avoid disappointment.
  8. Portability of the software.
    - Portability refers to whether a program can be copied or installed in more than one computer.
    - The software should be Portable, i.e. it should also be able to run on several different types of computers with very little or no modification (without re-writing the code).
    Note. Although, most software in the market today are portable, some developers produce software which can be installed on one machine only. This means that, if one has, say 20 computers, he/she should buy a license for each.
  9. Standards of the software.
    - The software should be standardized, i.e. the version of the program should not be too low or too high.
  10. Popularity of the software.
    - Before buying particular software, its current users should be interviewed to find out whether the software is successful and famous in the market.


Acquisition (Procurement) of a Computer.

Introduction.

  • Introducing a computer into the business is an act that should be considered with great concern, because it involves capital expenditure, and as such, it should only be done if it is necessary and its acquisition should be in a cost-effective manner.
  • Before acquiring the computer and its related facilities, one should investigate the effects of introducing the computer into the organization. This is to ensure that adequate returns are expected from such an investment.

Computer costs.

  • The cost of introducing a computer into the organization depends on Size, Nature & the application requirements of the affected organization.
  • Small & simple organizations may require less sophisticated computer installations. Big & complex business organizations may require complex configuration and sophisticated related facilities.
  • The costs for installing a computer system may be classified as;
    • Initial costs.
    • Recurrent costs.

Initial costs.

  • This is the initial capital expenditure onto the computer facilities when they are being acquired.
  • These costs depend on the Type, Nature and the Model of the facilities to be acquired.
  • The costs are influenced by the method used to acquire the computer and its related facilities.
  • The organization should consider ways or plans of acquiring the following facilities:
    Facility Examples
    Hardware C.P.U and Peripherals
    Software System and Application programs
    Storage Media Tapes, Disks, Cassettes, etc.
    Training Managers, Analysts, Programmers, Operators, etc.
    Computer room  Construction, Environmental conditions, Equipments, etc.
    Others Feasibility study, Programming, Changeover costs, etc.

Recurrent costs.

  • Once the computer facilities have been acquired and the system becomes operational, the operating costs for the computer system have to be met by the organization.

Examples of such costs are:

  1. Depreciation costs the charges on depreciating machines & other equipments, e.g., Air conditioning facilities.
  2. Wages of staff, e.g., Analysts, Programmers, Operators, etc.
  3. Administration expenses, e.g., Telephone bills, Insurance cover, consumable costs, etc.
  4. Other general expenses, e.g. conducting seminars, on-job training for staff, etc

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