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Computer Science


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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;

  • 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.


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


A Computer system consists (or is made up) of 4 basic elements that are interrelated and work in unison.  The four elements are:

  • Hardware.
  • Software.
  • Liveware (Computer user).


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:-

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.


* 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.

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.

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.


* Screen (Monitor/ Visual Display unit – VDU).                         * Printers                    

* Audio Response units.                                                               * Graph Plotters.                    

* Sound output devices, e.g. Speakers.                                        * Microforms.

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 inthe way (technology) they store data & the capacities of data they can hold.

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.


  • 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 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;



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.

                          Bus                                                                            Bus     


                                                Fig. 1.2: 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.


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. 


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.


  1. Give THREE main functions of a computer input device.
  2. State four examples of input devices you know.

Classification of Input devices.

Input devices can be classified according to how they are used to enter data into a computer.  These include.

  • Keying devices.
  • Pointing devices such as the Mouse, Trackball, etc.
  • 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.

  • Speech recognition or Voice input devices such as Microphones.
  • Touch screen and Digitizers.


Type of keying devices

  • Traditional keyboard
  • Flexible keyboard
  • Ergonomic keyboard
  • keypad.


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.


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.
  • 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.


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.


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.


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.


  • 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.


These are hand-held Input devices, which enable the user to interact with a program.  They are used for playing computer games.

A 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.

A 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.


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.


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;

  • 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.
  • 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.
  • By Banks & Insurance companies to verify signatures.  A signature written on a pad is compared against another formerly stored in the computer.
  • Pads are also good at detecting forgeries.


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.


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.

  • Voice input is a fast & easier method mostly suitable for the handicapped especially those with impaired hands.
  • 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.

  • In Voice-activated toys & games.
  • 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.

  • In Automated materials handling – in airports, handler’s give spoken commands that direct the luggage to the appropriate conveyor belt.
  • 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.
  • 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.

  • 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.

  • 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).

  • 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.

  • Speech input is complex to develop & is still at the early stages of development.

Review Questions.

  1. Explain briefly how the following types of devices work.
    1. Speech recognition.
    1. Graphic (digitizing) tablet.
    1. Touch sensitive screen.
    1. Light pen.
  2. State TWO advantages and TWO disadvantages of using Speech recognition devices.


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


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 adesktop machine that looks like a small photocopier.  It scans a whole page at a time.  An example is the Flatbed scan

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 word-processor, 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.
  • The light on the scanning window cannot turn off.

This shows that there is a conflict with resident software on DMA channel.

  • 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.

  • The Scanner turns off as soon as you start scanning.

This shows there might not be enough RAM to scan the images.

  • 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.


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: –

  • Marks – short lines made by hand, usually in pencil on a document.
  • Characters – hand-written (e.g. on meter-reading) or printed in magnetic ink on cheques.
  • Printed lines – e.g. the bar codes.

Document readers can be classified into; Optical readers and Magnetic Readers.

Optical Readers.

Optical readersuse 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 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 re-used 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.

  • The document should be handled carefully (e.g. it should not be folded or creased) for accurate reading.
  • Document size & type area may be limited for accurate reading.
  • 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.


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.

  • 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.

  • They read data directly from the source document & therefore, no data preparation is required. 
  • Errors are easily corrected.
  • The documents can be re-used, thus saving on stationery.
  • The contents of the documents are both human & machine sensible, hence reliable.
  • The sensitivity of an OMR can be altered to allow for different surface, pencils and inks.
  • OMR has a better recognition rate than OCR.
  • With an OCR, no typing or transcription/recording process is involved & therefore, not prone to transcription errors.

Comparative disadvantages of OMR and OCR.

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


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.

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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.

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


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.


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, Address, Telephone 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.

  • 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.
    • It is a cost-saving method.
    • 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.
    • Does not require special skills to operate.
    • It improves customer convenience.

Disadvantages of using a Bar-code reader.

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


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.


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


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


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 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.


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.


Sensors are devices that can be connected to computers & are used to record physical quantities like Temperature, light, humidity.

Examples of direct input instruments: – (COMPUTER SYSTEMS.)

  • Sensors used to record temperature, light, humidity in a Green house to ensure the best conditions for plant growth.
  • Thermostats connected to a Central heating system controlled by a computer in order to monitor temperature & to help save electricity.
  • Pressure pads on a road connected to computer-controlled traffic lights to speed traffic flow.
  • 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.

  • 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.
  • No typing or recording required, and therefore, not prone to transcription errors.
  • The documents can be re-used, thus saving on stationery.
  • The contents of the documents are both human & machine sensible, hence reliable.
  • Errors are easily corrected.
  • Difficult to forge.

Review Questions.

  1. (a). What are document readers?

(b). Describe various kinds of document readers.

  • (a). What is the difference between OCR and OMR?

(b). State two advantages & two disadvantages of each.

  • The diagram below shows coded data that could be input into a computer.
coded data
  • What is the name given to the above method of input?
    • State TWO applications that would use this method.
    • For one of the applications you have given, state TWO items of information that might be represented by the coded data.
    • State what hardware is needed to enter the coded information into a computer and briefly describe how this hardware works.
  • Explain the advantages and disadvantages of the following:
    • OCR.
    • OMR.
    • MICR.

Interactive whiteboard

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