DATA PROCESSING - Computer Studies Form 3 Notes

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  • Data refers to the raw facts that do not have much meaning to the user and may include numbers, letters, symbols, sound or images.
  • Information, on the other hand, refers to the meaningful output obtained after processing the data.
  • Therefore the data processing refers to the process of transforming raw data into meaningful output i.e. information.
  • Data processing can be done manually using pen and paper, mechanically using simple devices like typewriters or electronically using modem data processing tools such as computers.
  • Electronic data processing has become so popular that manual and mechanical methods are being pushed to obsolescence.

Data Processing Cycle

  • Data processing cycle refers to input-process-output stages that data goes through to be transformed into information.
  • It is often referred to as a cycle because the output obtained can be stored after processing and may be used in future as input.
  • The four main stages of data processing cycle are:
    • Data collection
    • Data input
    • Processing
    • Output

Data Collection

  • Data collection is also referred to as data gathering or fact-finding.
  • It involves looking for crucial facts needed for processing.

Methods of Data Collection

  • Some methods of data collection include interviews, use of questionnaires, observation etc.
  • In most cases, the data is collected after sampling.
  • Sampling is the process of selecting representative elements (e.g. people, organisations) from an entire group (population) of interest.
  • Some of the tools that help in the data collection include source documents such as forms, data capture devices such as a digital camera etc.

Stages of data collection

  • The process of data collection may involve a number of stages depending on the method used.
  • These include:
    • Data creation: This is the process of putting together facts in an organised format. This may be in form of manually prepared document or captured from the source using a data capture device such as a bar code reader.
    • Data transmission: This will depend on whether data need to be transmitted via communication media to the central office.
    • Data preparation: This is transcription (conversion) of data from source document to machine-readable form. This may not be the case for all input devices. Data collected using devices that directly capture data in digital form do not require transcription.
    • Media conversion: Data may need to be converted from one medium to another e.g. from a flash disk to hard disk for faster input.
    • Input validation: Data entered into the computer is subjected to validity checks by a computer program before being processed to reduce errors at the input.
    • Sorting: In case the data needs to be arranged in a predefined order, it is first sorted before processing.

Data Input

  • Data input refers to a process where the collected data is converted from human readable form to machine-readable form (binary form).
  • The conversion takes place in the input device.


  • This is the transformation of input data by the central processing unit (CPU) to a more meaningful output (information).
  • Some of the operations performed on data include calculations, comparing values and sorting.


  • The final activity in data processing cycle is producing the desired output also referred to as information.
  • The information can then be distributed to the target group or stored for future use.
  • Distribution is making the information available to those who need it and is sometimes called information dissemination.
  • This process of dissemination may involve electronic presentation over radio or television, distribution of hard copies, broadcasting messages over the Internet or mobile phones etc.

Description of Errors in Data Processing

  • The accuracy of computer output is very critical. As the saying goes, garbage in, garbage out (GIGO), the accuracy of the data entered in the computer directly determines the accuracy of the information given out.
  • Some of the errors that influence the accuracy of data input and information output include transcription, computation and algorithm errors.

Transcription Errors

  • Transcription errors occur during data entry. Such errors include misreading and transposition errors.

    Misreading errors
    • Incorrect reading of the source document by the user and hence entering wrong values bring about misreading errors. For example, a user may misread a hand written figure such as 589 and type S86 instead i.e. confusing 5 for S.

    Transposition errors
    • Transposition errors results from incorrect arrangement of characters i.e. putting characters in the wrong order. For example, the user may enter 396 instead of369.
  • Transcription errors can be avoided by using modem data capture devices such as bar code readers, optical character readers, and digital cameras etc., which enter data with minimum user intervention.

Computational Errors

  • Computational errors occur when an arithmetic operation does not produce the expected results.
  • The most common computation errors include overflow, truncation and rounding errors.

Overflow errors

  • An overflow occurs if the result from a calculation is too large to be stored in the allocated memory space. For example if a byte is represented using 8 bits, an overflow will occur if the result of a calculation gives a 9-bit number.

Truncation errors

  • Truncation errors result from having real numbers that have a long fractional part that cannot fit in the allocated memory space. The computer would truncate or cut off the extra characters from the fractional part. For example, a number like 0.784969 can be truncated to four digits to become 0.784. The resulting number is not rounded off.

Rounding errors

  • Rounding errors results from raising or lowering a digit in a real number to the required rounded number. For example, to round off 30 666 to one decimal place, we raise the first digit after the decimal point if its successor is more than 5. In this case, the successor is 6 therefore 30.666 rounded up to one decimal place is 30.7. If the successor is below 5, e.g. 30.635, we round down the number to 30.6.

Algorithm or Logical Errors

  • An algorithm is a set of procedural steps followed to solve a given problem. Algorithms are used as design tools when writing programs. Wrongly designed programs would result in a program that runs but gives erroneous output. Such errors that result from wrong algorithm design are referred to as algorithm or logical errors.

Data Integrity

  • Data integrity refers to the accuracy and completeness of data entered in a computer or received from the information system. Integrity is measured in terms of accuracy, timeliness and relevance of data.


  • Accuracy refers to how close an approximation is to an actual value. As long as the correct instructions and data are entered, computers produce accurate results efficiently. In numbers, the accuracy of a real number depends on the number. For example 72.1264 is more accurate than 72.13.


  • Timeliness of data and information is important because data and information have a time value attached to them. If received late, information may have become meaningless to the user. For example, information on the newspaper that is meant to invite people for a meeting or occasion must be printed prior to the event and not later.


  • Data entered into the computer must be relevant in order to get the expected output. In this case, relevance means that the data entered must be pertinent to the processing needs at hand and must meet the requirements of the processing cycle. The user also needs relevant information for daily operations or decision making.


Threat to Data Integrity

- Threats to data integrity can be minimized through the following ways:

  1. Backup data preferably on external storage media.
  2. Control access to data by enforcing security measures.
  3. Design user interfaces that minimize chances of invalid data entry.
  4. Using error detection and correction software when transmitting data.
  5. Using devices that directly capture data from the source such as bar code readers, digital cameras, optical character readers etc.

Data Processing Methods.

  • As mentioned earlier, data can be processed manually, mechanically or electronically.

Manual Data Processing

  • In manual data processing, most tasks are done manually with a pen and a paper. For example in a busy office, incoming tasks (input) are stacked in the "in tray". The processed tasks are then put in the "out tray" (output). The processing of each task involves a person using the brain in order to respond to queries. The processed information from the out tray is then distributed to the people who need it or stored in a file cabinet.

Mechanical Data Processing

  • Manual processing is cumbersome and boring especially when processing repetitive tasks. Mechanical devices were developed to help in automation of manual tasks. Examples of mechanical devices include the typewriter, printing press and weaving looms. Initially, these devices did not have any electronic intelligence.

Electronic Data Processing

  • For a long time, scientists have researched on how to develop machines or devices that would simulate some form of human intelligence during data and information processing. This was made possible to some extent with the development of electronic programmable devices such as computers.
  • The advent of microprocessor technology has greatly enhanced data processing efficiency and capability. Some of the microprocessor-controlled devices include computers, cellular (mobile) phones, calculators, fuel pumps, modem television sets, washing machines etc.

Computer Files

  • A file can be defined as a collection of related records that give a complete set of information about a certain item or entity. A file can be stored manually in a file cabinet or electronically in computer storage devices. Computerized storage offers a much better way of holding information than the manual filing systems, which heavily rely on the concept of the file cabinet.

Some of the advantages of computerized filing system include:

  1. Information takes up much less space than the manual filing.
  2. It is much easier to update or modify information.
  3. It offers faster access and retrieval of data.
  4. It enhances data integrity and reduces duplication.

Elements of a Computer File

  • A computer file is made up of three elements namely: characters, fields and records.
    • Characters - A character is the smallest element in a computer file and refers to a letter, number or symbol that can be entered, stored and output by a computer. A character is made up of a set of seven or eight bits depending on the character-coding scheme used.
    • Fields - A field is a single character or collection of characters that represents a single piece of data. For example, in a student’s record, the student's admission number is an example of a field.
    • Records - A record is a collection of related fields that represent a single entity. For example, in a class score sheet, details of each student in a row such as admission number, name, total marks and position make up a record.

Logical and Physical Files

  • Computer files are classified as either logical or physical.

Logical files

  • A logical file is a type of file viewed in terms of what data items it contains and details of what processing operations may be performed on the data items. It does not have implementation specific information like field, data types, size and file type. Logical files are discussed in system design later in the book.

Physical files

  • As opposed to a logical file, a physical file is one that is viewed in terms of how data is stored on a storage media and how the processing operations are made possible. Physical files have implementation specific details such as characters per field and data type for each field. Physical files are discussed later in system implementation and operation in this book.

Types of Computer Processing Files

  • There are numerous types of files used for storing data needed for processing, reference or backup.
  • The main common types of processing files include master files, transaction, reference, backup, report and sort file.

Master File

  • A master file is the main file that contains relatively permanent records about particular items or entries. For example a customer file will contain details of a customer such as customer ID, name and contact address.

Transaction (Movement) File

  • A transaction file is used to hold input data during transaction processing. The file is later used to update the master file and audit daily, weekly or monthly transactions. For example in a busy supermarket, daily sales are recorded on a transaction file and later used to update the stock file. The file is also used by the management to check on the daily or periodic transactions.

Reference File

  • A reference file is mainly used for reference or look-up purposes. Lookup information is that information which is stored in a separate file but is required during processing. For example, in a point of sale terminal, the item code entered either manually or using a bar code reader looks up the item description and price from a reference file stored on a storage device.

Backup File

  • A backup file is used to hold copies (backups) of data or information from the computers fixed storage (hard disk). Since a file held on the hard disk may be corrupted, lost or changed accidentally, it is necessary to keep copies of the recently updated files. In case of the hard disk failure, a backup file can be used to reconstruct the original file.

Report File

  • A report file is used to store relatively permanent records extracted from the master file or generated after processing. For example you may obtain a stock levels report generated from an inventory system while a copy of the report will be stored in the report file.

Sort File

  • A sort file is mainly used where data is to be processed sequentially. In sequential processing, data or records are first sorted and held on a magnetic tape before updating the maste file.

File Organization Methods

  • File organization refers to the way data is stored in a file. File organization is very important because it determines the method of access, efficiency, flexibility and storage devices to be used.
  • There are four methods of organizing files on a storage media. This includes: sequential, random, serial and indexed-sequential

Sequential File Organisation

  • In sequential file organisation, records are stored and accessed in a particular order sorted using a key field. Retrieval requires searching sequentially through the entire file record by record from the beginning to the end. Because the records in the file are sorted in a particular order, better file searching methods like the binary search technique can be used to reduce the time used for searching a file. Since the records are sorted, it is possible to know in which half of the file a particular record being searched is located. Hence this method repeatedly divides the set of records in the file into two halves and searches only the half in which the record is found. For example, if the file has records with key fields 20, 30, 40, 50, 60 and the computer is searching for a record with key field 50, it starts at 40 upwards in its search, ignoring the first half of the set.

Random or Direct File Organisation

  • In random or direct file organisation, records are stored randomly but accessed directly. To access a file stored randomly, a record key is used to determine where a record is stored on the storage media. Magnetic and optical disks allow data to be stored and accessed randomly.

Serial File Organisation

  • With serial file organisation, records in a file are stored and accessed one after another. The records are not sorted in any way on the storage medium. This type of organisation is mostly used on magnetic tapes.


Indexed-sequential File Organisation Method

  • This method is almost similar to sequential method, only that an index is used to enable the computer to locate individual records on the storage media. For example, on an magnetic drum, records are stored sequentially on the tracks. However, each record is assigned an index that can be used to access it directly.

Electronic Data Processing Modes

- There are several ways in which a computer, under the influence of an operating system is designed to process data. Examples of processing modes are:

  1. Online processing
  2. Real-time processing
  3. Distributed processing
  4. Time-sharing.
  5. Batch processing
  6. Multiprocessing
  7. Multitasking
  8. Interactive processing

On-line Processing

  • In online data processing data is processed immediately it is received the computer is connected directly to the data input unit via a communication link. The data input may be a network terminal or an online input device attached to the computer.

Real-time Processing

  • In a real-time data processing, computer processes the incom111g data as soon as it occurs, up-dates the transaction file and gives an immediate response that would affect the events as they happen. This is different from online in that for the latter an immediate response may not be required. The main purpose of a real-time processing is to provide accurate, up-to-date information hence better services based on a true (real) situation. An example of real-time processing is making a reservation for airline seats. A customer may request for an airline booking information through a remote terminal and the requested information will be given out within no time by the reservation system. If a booking is made, the system immediately updates the reservations file to avoid double booking and sends the response back to the customer immediately.

Distributed Data Processing

  • Distributed data processing refers to dividing (distributing) processing tasks to two or more computers that are located on physically separate sites but connected by data transmission media. For example, a distributed database will have different tables of the same database residing on separate computers and processed there as need arises. The users of the distributed database will be completely unaware of the distribution and will interact with the database as if all of it was on their computer.. This distribution of processing power increases efficiency and speed of processing. An example is in the banking industry where customers' accounts are operated on servers in the branches but all the branch accounts can be administered centrally from the main server as if they resided on it. In this case, we say that the distributed database is transparent to the user because the distribution is hidden from the user's point of view.


  • In a time-sharing processing, many terminals connected to a central computer are given access to the central processing unit apparently at the same time. However in actual sense, each user is allocated a time slice of the CPU in sequence. The amount of time allocated to each user is controlled by a multi-user operating system. If a user's task is not completed during the allocated time slice, he/she is allocated another time slice later in a round robin manner.

Batch Processing

  • In batch processing, data is accumulated as a group (batch) over a specified period of time e.g. daily, weekly or monthly. The batch is then processed at once. For example in a payroll processing system, employees' details concerning number of hours worked, rate of pay, and other details are collected for a period of time, say one month. These details are then used to process the payment for the duration worked. Most printing systems use the batch processing to print documents.


  • Multiprocessing refers to the processing of more than one task at the same time on different processors of the same computer. This is possible in computers such as mainframes and network servers. In such systems, a computer may contain more than one independent central processing unit, which works together in a coordinated way. At a given time, the processors may execute instructions from two or more different programs or from different parts of one program simultaneously. This coordination is made possible by a multiprocessing operating system that enables different processors to operate together and share the same memory.


  • Multiprogramming, also referred to as multi-tasking refers to a type of processing where more than one programs are executed apparently at the same time by a single central processing unit. It is important to note that, as opposed to multiprocessing. In multiprogramming, a computer has only one central processing unit. The operating system allocates each program a time slice and decides what order they will be executed. This scheduling is done so quickly that the user gets the impression that all programs are being executed at the same time.

Interactive Processing

  • In interactive data processing, there is continuous dialogue between the user and the computer. As the program executes, it keeps on prompting the user to provide input or respond to prompts displayed on the screen.
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