computer hardware

The central processing unit CPU

The Control Unit.

It is known as the nerve centre of a computer system. It controls, supervises o, oversees all the activities of the computer and monitors the execution of any program processed.  Its primary function is to select and interpret instructions and to send appropriate signals to other units in the computer for their execution.  Other functions include:-

1.     Co-coordinating and controlling various parts of the computer i.e. main memory A.L.U. Peripheral devices (outside)

2.     Control transfer of data to and from the working storage area.

3.     Retrieve and decode programs instructions from the internal storage in their correct sequences interpret these instructions and make the computer to execute the instructions. 

4.     Connect the required circuits to enable the Arithmetic Unit to process the data storage as specified by the program.

5.     Control the activities of all the other units of the computer by using appropriate control signals.

6.     Automatically repeat this circle of operations till either it’s instructed to stop or the last instruction has been executed.

7.     Determines the location of the CPU memory of the next instruction to be retrieved.

Arithmetic logic control

It contains a large number of electronic circuits which help to carry out a variety of arithmetic logic functions under the direction and command of the control unit.  It consists of two units:-

1.     Arithmetic unit / sect.

2.     Logic unit/ section.

The AU carries out arithmetic operations which include addition multiplication, subtraction, division etc.

The logic unit carries out logic operations which include arrangements and rearrangements e.g. sorting, matching, comparing etc.

Main memory

It is made up of by stable elements that hold data instructions or information in a two state form i.e. Binary notation zeros (0s) and ones (1s) .it hold data and instructions during processing and also intermediate results before they are relayed to the output device

Main memory classification

They are two sections:-

1.     Random Access Memory (RAM)

2.     Read Only Memory (ROM)

Random Access Memory (RAM)

The contents of these memory sections are readily available for retrieval.  Its volatile i.e. contents are lost when power goes off.  It contributes to about 70% of the internal memory.  It can also be referred to as it is possible to transfer data or instructions to or from it.  Writing is transferring to memory.

Main Functions

1.     Store data and instructions awaiting process.

2.     Store instructions being obeyed or whose parts have been obeyed.

3.     Store intermediate results before they are communicated to their recipients.

Read – only memory (ROM)

The contents of this memory section can only be retrieved (read) but can’t be altered.  Its non-volatile i.e. it doesn’t lose its contents loose its contents when power goes off.  It contributes to 30% of the internal memory.

Main Functions

1.     It stores data and instruction that are necessary fro the normal functions of the computer system. Hardware.

2.     Stores the controlled program that’s necessary for the initial activation of the hardware on power switch on.

Input devices

These are devices that take in data and instructions that people can read and covert them to a form that the computer can process.  The type of input device selected depends on the computer installed and the associated processing requirements e.g. Real time , Batch Processing Mode etc.

 Examples of input Devices;

1.     Visual display unit – VDU

It’s got the keyboard for data and instruction input. It’s of QWERTY type- keys. It also has a screen which displays information (in a page of typically 24 rows and eighty columns). This displayed information can be highlighted by change the background blinking different levels of brightness or by using different colour displays.

2.     The mouse

It’s a hand held device with point and click capabilities that’s usually connected to a computer by a cable.

3.     Touch screen

Allows users to enter limited amounts of data by touching the surface of a sanctified video displays monitor with a figure or a pointer.

4.     Digital scanner

Translates images such as pictures or documents into digital form and is an essential component of image processing systems.

5.     Audio input

Voice input devices that convert spoken words into digital form for processing by the computer e.g. the microphone.

6.     The light Pen

It’s a light sensitive stylus or pen like device connected by a wire to the computer turning terminal the user brings to the pen to the desired point to the desired screen and presses the pen button which identifies that screen location to the computer.  It’s mainly used by engineers or graphic designers.

Document Readers

They are devices that directly send data from the source document then convey them to go as computer input directly in terms of electronic signals with no requirement for verification because the transcription process is not involved.

They are grouped into:-

1.     Optical document readers.

2.     Magnetic document readers.

Optical document reader ODR

They use the principle of light to sense document contents and are of two versions, i.e. Optical Character Reader or Optical character recognition (OCR)

They are devices that translate specially designed marks, characters and codes into digital from.  The most lately used optical used is the bar code which is used in point of sales system in supermarkets.  The codes can include date, time, and location of data in addition to identification data.

Optical mark read OMR

The technical involves use of standard represented documents that are marked either a black positions.  The position of each mark is determined by deciding the form into various mark has a meaning which is depend upon its position :


1.     No typing or transcription requirements hence error frees.

2.     Documents are turned around hence save of stationery.

3.     Contents of documents are both human and machine sensible hence reliable.

4.     It provides a fast input as compared to e.g. Keyboard devices.


1.     It’s an expensive method of input because of specialized techniques and requirement.

2.     Document size and type area may be limited for accurate reading.

3.     Special typing or character formation and paper quality may be crucial.

4.     Handling information is necessity e.g. documents should not be folded for accurate reading.

The Magnetic Document Readers

-          It is used the principle of magnetism to send document contents written using magnetic character reader recognition (MICR).

-          The MICR used to read magnetized characters or documents and translate them into digital form.  The ink contains Iron II Oxide and so by magnetizing when reading into the MICR, characters become recognizable.  It is used primarily in cheque processing from the banking industry.  Characters on the bottom of a cheque identify the cheque i.e. bank code, branch code and customer A/C No.

Output Devices

The quality of a computer system can be best accessed by the quality of output it generates.  The quality, validity and usefulness of output are influenced by the output facility used.  Therefore output devices are used to provide the user with the results of processing which may need to be processed in future.

Monitor VDU

It gives a soft copy output that can easily be accessed and edited.  Its classified as:-

  1. Monochrome

-          Use one for foreground representation of characters.

  1. Coloured monitor

-          Represents output using more than two colours.


-          It produces a hard copy output on paper which is permanent and is desirable for information or results of computer working which can be maintained for future reference. When selecting the printer consider the cost, volume of printing expected, print quality and interface with the other computer systems.  Printers can be classified as:-

Secondary Storage Devices

They are used for long term storage of data.  They include one magnetic disc.  They are of two types; floppy disc & hard disc.

2)     Floppy disc

Are portable with lower storage capacities and access rate than hard disc.  They are useful for systems requiring rapid and direct access to data. 

3)     Optical discs

They use laser technology to store massive qualities of data in a highly compact form.  The most common optical disc systems with PCs are the CD (Compact Disk).  They are appropriate for applications where enormous quantity of unchanging data must be stored compactly for easy retrieval or for applications combining text, sound and images.


1. CD-ROM (CD-R)

IT’S A read only storage i.e. no new data can be written to it, if can only be read.

2. CD -Recordable (CD-R)

It allows users to record data only once to once written the data can't be erased but can be read indefinitely.


Allows users to create re-writable optical discs for applications requiring carry volume of storage where the information is occasionally updated.

4. Digital Video (versatile) Disc

it also utilizes laser technology to store data . They are off higher capacity than CDs and can store fuller length motion pictures and large amounts of data.  They are replacing CDs because they can store large amounts of digitized texts, graphics, audio and video data.

Once read only, writable and re-writable DVDs are now available.

5. Magnetic tapes

It’s a thin plastic tape on which data represented with magnetized ports.  they store data sequentially (serial access storage devices)

6. Flash discs

They utilize semi-conductor technology to store data i.e. the flip flop They are small, light in weight, removable and re-writable. They have a debased form of storage more than DVDs

7.     Worm discs (write once read many)

they can be written or recorded on to just once after which they cannot be erased but can be read many times ... It’s more suitable for storing back up files and archived files.  They have large volumes than CD-R and magnetic tapes.


1.         Adequacy of memory size

2.         The number of backing storage required.

3.         The type of backing storage required and capacity.

4.         The output devices required and their operating space.

5.         The possibility of expansion of the memory.

6.         The possibility of enhancing the configuration with extra input/output storage peripherals.

7.         The performance types of CPU and the peripherals.

Computer Software

A computer software are the details instructions that control the operation of a computer system.  . They instruct the computer to the computer. They instruct the computer on what to do and how to do it.

Classification of computer software

1. System Software
 – it’s a set of programs which have been developed and installed in a computers system for the purpose of developing other programs and to enhance the functional capabilities of a computer system. They are developed and installed by the manufacturer of the computer system hardware. It is classified into two.

(i)             operating system

(ii)            Utility programs or system utilities.

Operating system.

It’s a suite of programs that manages the computer resource such as input output transfers, memory, CPU ….

System utilities and Utility programs
They are used frequently to carry out routine job e.g. sorting, merging, debugging and are normally supplied by the manufacturer..
2..Application software

These programs which help the computer to work efficiently for specific application. They help develop to handle the organization application requirements. They are sub classified to

(i)             Application packages.

(ii)            User programs.

Application packages.

They are off shelf programs developed and supplied by computer manufacturer or software houses at a price. They are developed to solve particular problems with no alternations. Some of the packages in great use are:-

  • Word processing software bIf allows used to create and documents electronically to meet a users specification e.g. Ms word, word perfect etc.
  •  Spread Sheet. They are variable for application in which numerous calculations with pieces of data must be related to each other. They are useful for applications that require modeling and what if analysis e.g. ms Excel.
  • Data management software  It is used for creating and manipulating lists, creating files and data basis and combining information for reports e.g. Ms Access Dbase.
  • Presentation graphics software It’s used to create professional quality graphics presentation e.g. Ms Power point

Advantages of computer packages

  1. They are well tested so that problems may not occur.
  2. They are menu drive. The user is guided on a set of optionalities as displayed on the screen.
  3. They are generally portable e.g. you can run it on different computer families.
  4. They can be rented out especially by users who require their services only periodically.
  5. Time that would have been spent in program development is saved.


  1. They might not fit well into the organizations processing tasks for they are intended to meet a variety of user needs.
  2. The user may not b free to correct any routines of the package because there is always a maintenance guarantee and the developers copyright Acts application.


(1)   Cost of a package in relation to the expected benefits.

(2)   Compatibility of the package within the existing computer resources i.e. hardware and software platforms.

(3)   Whether there is maintenance support from the suppliers (guarantee)

(4)   Whether there is accompanying documentation which helps in suing maintaining and installing the package (Manual)

(5)   Portability of the package i.e. can be used in different computers families.

(6)   Ease of learning and suing the package. The duration and cost of training is considered.

(7)   How successful is it in the market.

3.User Programs

They are in-house programs (tailor made0 developed to solve specific processing tasks within the organization and may not suit the other organization needs e.g. a payroll.

Advantages of user programs

·         Their processing tasks are aligned to the organization needs

·         User program tend to secure data handling platform than applicator packages


·         A lot of time is spant on program development

·         They are prone to errors

·         They might be very expensive than application packages

 Programming Languages
A computer program is a set of instructions given to the computer to perform various specified operations. At present, the following programming languages are on use though research continues.
  1. The machine language
  2. The assembly or low level language
  3. The high level language (3GM)


It’s expressed in binary digits Os and 1s
  • program execution is fast
  •  programming in machine language was a very slow labour intensive process. 
  • Programs are machine dependent hence difficult to be executed by a machine of a different family.


They use mnemonics which are easy to remember. Comments may incorporated in the program statement to make them easier to be understood by human programmers.
  •    It reduces the time required to develop a program as compared to machine language
  •  It is easier to understand , use and modify  a program as compared to machine language
  • Programs are still machine dependent hence non portable.
  • Programmers are still strained in leaning and subsequent program rating. 
  • Programs written in assembly language are slow since thwy have to be translated into their project code equivalent before they can be obeyed by the computer hardware.


Its main language is very close to the human being natural language vocabulary hence easy to understand and use. It allows problem solution to be specified in a human and problem oriented manner.
  •  program are easier to develop and maintain
  •  Three 3GL programs are self Documentary i.e. program statement display transparency of purpose and hence program verification is eased. Thus leading to high program reliability.
  •   Programs are machine independent hence portable
  • They are less efficient in the use of CPU and related facilities. As they are not machine oriented
  • they are slow due to need of translation to a language a computer can understand
  •   Execution time – machine language executes fast since no translation is needed
  •  Development time _the use of  first and second generational languages took a lot of time to develop an application
  •  Maintenance – it was not easy to maintain programs made using first and second generational language
  • Availability of programmers-some languages tend to have low skills availability
  • The OS in use-some programming languages can run on all OS versions others cant