Introduction to Computers

Physical Parts of a Computer

Objectives By the end of this lesson, you should be able to: State and explain various physical parts of a computer

Physical Parts of a Computer

Keyboard - it is a keying input device used to enter data into a computer

system unit - this is the box-like casing that houses the CPU  and the motherboard together with other electronic components. System units are of two types namely:

  1. Tower
  2. Desktop

Mouse - is a pointing input device used to move the pointer on the screen and also used to execute commands by pressing its buttons

Monitor - used to display results of information processing (output) and running programs.

Peripheral devices - refers to the physical devices connected to the systems through ports e.g printers, speakers, flash disks, keyboards, monitors

Definition of a computer

Objectives By the end of this lesson, you should be able to: Define a computer Differentiate between data and information Explain the unique characteristics of computer as a data processing tool

Definition of a computer

  • A computer is  an electronic device that receives the user's input (data)  and processes it under the influence of computer programs(software) to produce information
  • A computer is a programmable electronic device that accepts raw data as input and processes it with a set of instructions (a program) to produce the result as output ( According to Java T Point)
  • An electronic device that accepts data, as input and transforms it under the influence of a set of special instructions called programs, to produce the desired output (referred to as information)

Data refers to raw facts without much meaning to the user while information refers to the processed data that is meaningful to the user

Software refers to a set of instructions that guides the computer on how to perform a given task

Characteristics of a Computer

1. Fast: A computer can perform calculations within seconds that human beings would take hours to complete

2. Accurate: A computer has a high degree of accuracy regardless of the complexity and number of times a calculation is performed. Errors may occur due to data inconsistency and inaccuracy

3. Versatile: Can be used to carry out different tasks with the same accuracy and efficiency such as playing games and performing calculations

4. Reliable: computers work for many years without any problem

5. Diligent: A computer can perform repetitive tasks without getting bored, tired, fatigued or losing concentration

6. Vast Storage Capacity: computers have inbuilt memory used to store and retrieve large amount of data

Classification of Computers Lesson I

By the end of this lesson you should be able to: Classify computers according to their physical sizes

Classification of Computers Lesson I

Classification According to Physical Size

  • Supercomputers
  • Mainframe Computers
  • Minicomputers
  • Microcomputers


It is the largest, fastest and most expensive. Used for scientific research and forecasting which involves a lot of calculations.


  • They are able to perform many complex calculations in a few seconds.
  • They are kept in a special room due to their extreme weight.
  • They process data in large quantities hence generating a lot of heat.
  • Supercomputers require special cooling systems.
  •  Supercomputers are mainly used for scientific research which requires huge calculations.
  • They have a very high storage capacity.
  •  Examples of supercomputers are CRAY T3D and NEC- 500
  • Supercomputers are mainly found in developed countries such as in USA where they are used for advanced scientific research such as nuclear physics.

Mainframe Computers

Less powerful compared to supercomputers but more powerful than minicomputers. The main difference between mainframe and supercomputers is that supercomputers channel their power into processing a few programs as fast as possible while mainframes channels their power into processing many programs simultaneously (parallel processing).

It supports many concurrent users

It is mainly for commercial applications i.e handling daily transactions and batch data processing

Characteristics of mainframe computers.

  • - They are physically smaller than supercomputers.
  • - Supports a large number of peripheral devices.
  • - They are less powerful and expensive as compared to supercomputers.
  • - They are used for processing data and performing complex mathematical calculations.
  • -  They have a high storage capacity as compared to minicomputers and microcomputers.
  • - Mainframe computers handle all kinds of problems whether scientific or commercial.
  • - They are kept in an air-conditioned environment in a special room.
  • They are mostly found in government agencies, big organizations and companies such as banks, hospitals, airports etc.
  • Some Examples of mainframe computers are IBM 4381, ICL 39 series, and CDC Cyber series.



It is less powerful than the mainframe but more powerful than microcomputers. It is smaller in size compared to a mainframe computer.

  1. They are physically smaller than mainframe computers.
  2. Supports fewer peripheral devices as compared to mainframe computers.
  3. They are less expensive as compared to supercomputers.
  4. Lower storage capacity compared to mainframe computers.
  5. Minicomputers are mainly used in business and commerce.
  6. An example of a minicomputer is PDP-8 launched in 1965
  7. They are heavily used as network servers up to date.


They are the smallest, cheapest, and least powerful. Examples are Desktop, laptops, tablets, smartphones, and smartwatches

Microcomputer is the smallest, cheapest and relatively least powerful type of computer. The term microcomputer evolved from the word microprocessor which is the brain of a micro-computer.

  • Microcomputers are also called personal computers (PC) because they are designed to be used by one person at a time.     
  • Microcomputers are commonly used in training and learning institutions, small business enterprises, hospitals, homes etc. smaller and smaller microcomputers have been introduced i.e.
  1. The desktop computer- It is designed to be placed on top of an office desk and it is not portable.
  2. The laptop computers – Designed to be used by placing it on the lap hence its name. It is portable like a briefcase.
  3. The palm top – It is small enough to fit in the pocket and can be held on the palm when being used.

NB: The above-mentioned microcomputers are arranged in descending order according to size.

Advantages of laptop computers

  1. They are portable
  2. Displays clear images which prevent eye strain.
  3. Laptop batteries serve as a built-in uninterruptible power supply.

Disadvantages of laptop computers

  1. Many laptops have similar memory capacities.
  2. Laptops have few connecting ports and no growth potential.
  3. Security - Laptops are easy to steal.

The image below is a supercomputer


By Trower, NASA: Supercomputer

Classification of Computers Lesson II

By the end of this lesson, you should be able to: Classify computers according to purpose Explain each of the category of computers above

Classification of computers according to purpose

According to purpose, computers are classified as:

  • General Purpose Computers
  • Special Purpose Computers                 

General Purpose Computers

These refer to computers capable of performing a variety of tasks since they can store and execute different programs.

Special Purpose Computers

These are computers designed to perform a specific task. For example, a play station is used for playing graphic-intensive video games

Special-purpose computers are designed to serve a particular purpose or accomplish one particular task. Such computers can perform no other task except the one they were meant to do.


  1. In a computer network where the host computer serves several other computers connected to it. (Mainframe computers)
  2. A special type of computer known as Front end processor (FEP) may be used to specialize in the work of network control. I.e. controlling data, instruction and communication between various workstations and the host computer.

NB: Mobile Phones and calculators are also classified as special-purpose computers because they were made to perform one major task. i.e. phones meant for communication only and electronic calculators to carry out calculations only

Dedicated purpose computers

These computers are designed to perform a wide variety of tasks though they are committed to some processing tasks. I.e. the computer can be dedicated to carrying out word-processing tasks only.

Classification of Computers Lesson III

By the end of the lesson, you should be able: Classify computers as either digital , analog or hybrid.

Classification of computers according to functionality

According to functionality computers are classified as:

  • Analog computers
  • Digital computers
  • Hybrid Computers

Analog computers

These are computers that process data that is continuous in nature. Examples of continuous data are variations in physical quantities E.g. temperature, heart beats humidity etc

Digital data is represented using values that do not have any transitional changes over time.

NB: This means that the data is processed at a very high speed and within no time the output is provided to the user.

The data is said to be discontinuous because one task must be accomplished so before starting the other task. i.e. Each letter typed using a microcomputer is converted into digital form and displayed on the screen after processing operations at a time.

Analog data/continuous data is represented using values that have transitional changes on time.

NB: This indicates that analog data take time to process as compared to digital data.

Digital Computers

These computers process data represented in terms of binary digits. The data processed by these computers are discrete.

Hybrid computers

Processes both analog and digital types of data.


  • Fuel pumps
  • Analog BP machine
  • ATM machine
  • refrigerator,
  • differential analyser
  • Slide Rules
  • seismometer
  • voltmeter
  • flight simulators
  • speedometer, etc.

Public Domain, Calculator, Special Purpose Computer


Historical Development of Computers

Objectives By the end of the lesson, you should be able to: Describe the historical development of mechanical computer

Historical Development of Computers

The first computers were people. However, due to the complexity of tasks, mechanical computers and electromechanical computers emerged. Examples of mechanical computers included: Abacus(Chinese and Babylonians), Napier's Bones (Scottish Mathematician, John Napier), Slide Rule(William Oughtred), Pascaline Machine(Blaise Pascal, French Mathematician), and finally Charles Babbage Invented the analytical and Difference engine.

After mechanical computers, electronic computers emerged. Examples Mark I, ENIAC, UNIVAC, EDSAC, PDP-1, Z-3, IBM 1400, IBM,360, Altair 8800, Honeywell

The first electronic computer was the Electronic Numerical Integrator and Computer

Electronic computer generations are divided into five :

First Generation  (1940-1956)   

The remarkable features were:

  • used vacuum tubes/thermionic valves for processing
  • consumed a lot of power
  • emitted a lot of heat
  • Examples included ENIAC-Electronic Numerical Integrator and Calculator and EDVAC -Electronic Discrete Variable Automatic Computer

Second Generator(1956-1953)

The remarkable features were:

  • used transistor for processing
  • -The computers consumed less power, produced less heat, were much faster, and more reliable than those made with vacuum tubes.
  • -They used Magnetic core memories.
  • -RAM Memory size expanded to 32 KB.
  • -Their operation speed increased to between 200,000 – 300,000 instructions per second.  Their speeds were measured in Microseconds.  E.g., a computer could perform 1 million additions per second, which was comparatively higher than that of the 1st generation computers.
  • -The computers were smaller in size & therefore, occupied less space compared to the 1st G computers.
  • -They were less costly than the 1st G computers.

Examples of 2nd Generation computers:


  • NCR 501, IBM 300, IBM 1401, IBM 7070, IBM 7094 Series & CDC-6600 Mainframe computers.
  • UNIVAC 1107.
  • HONEYWELL 200.

Examples of computers developed in this generation included: PDP-1, IBM 1400

Third Generation(1964-1971)


  • Integrated Circuit (IC) was introduced
  • The processing speed increased to 5 Million instructions per second (5 MIPS).
  • -The storage capacity of the computers (i.e., the RAM memory sizes) expanded to 2 MB.
  • -They were smaller in size compared to 2nd generation computers.
  • -The computers used a wide range of peripheral devices.
  • -The computers could support more than user at the same time.  They were also able to support remote communication facilities.
  • -Magnetic disks were developed for storage purposes.
  • -The 1st microcomputer was produced during this period (1974).

Examples included: PDP-8 and IBM 360

Fourth Generation(1971-1990)

  • introduction of Very Large Scale Integrated Circuits (VLSI)
  • -The computers were small, and very fast.  Their processing speeds increased to 50 Million instructions per second.
  • -Had large storage capacity, i.e., their memory sizes expanded to several hundred Megabytes.
  • -Memories used included Magnetic disks, Bubble memories & Optical disks.

Examples of 4th Generation computers:


  • IBM 308 and 4300;
  • Amdahl 580
  • Honeywell DPS-88
  • Burroughs 7700, and the 16-bit & 32-bit microcomputers.  The first microcomputer was called Apple II
  • the first microcomputer was introduced

Examples Altair 8800

Fifth Generation (1990-Present)

In this generation fall today’s computers.

The technologies used  Parallel architectures, 3-Dimensional circuit design & superconducting materials.  These technologies have led to the development of computers referred to as Supercomputers, which are very powerful, and have very high processing speeds.  Their speeds are measured in Nanoseconds & Picoseconds.


They are able to perform parallel (or multi-processing) whereby a single task is split among a number of processors.

The memory sizes range between  1 Gigabyte & 1 Terabyte or more.

The computers are designed using VLSI and the Microchip technology that has given rise to the smaller computers, known as Microcomputers used today.

The computers have special instruction sets that allow them to support complex programs that mimic human intelligence often referred to as Artificial Intelligence.  Such programs can help managers to make decisions and also provide critical expert services to users instead of relying on human professionals.

  • massive processing power
  • parallel processing
  • use of artificial intelligence




Computer Laboratory

Objectives By the end of this lesson, you should be able to: Define computer laboratory State the factors that should be considered when setting up a computer lab State and explain measures to protect the computers and computer users

Definition of a computer laboratory

A computer laboratory is a special room set aside for the safe installation and use of computers

Factors to consider when setting up a computer laboratory:

  1. Security of the computer software and hardware
  2. The reliability of the power source
  3. The floor, space and number of computers to be set up
  4. The maximum number of users

Safety precautions and practices

Measures that protect the computer user

  1. The power cables should be well insulated to protect the user from the dangers of  electric shock
  2. users should be provided with standard ergonomic furniture to avoid health risks like back strain and fatigue which may result due to poor sitting positions. The furniture must have an upright backrest and should be high enough to position the eye at the same level as the computer screen.
  3. The room should be properly ventilated to avoid dizziness caused by a lack of enough oxygen
  4. The walls of the computer should not be painted with overbright paints
  5. The computer screens should face away from windows to avoid glare caused by bright backgrounds
  6. Overcrowding should be avoided since it may lead to suffocation

Measures that protect the computer

  1. The computer room should be burglar proofed by reinforcing windows, roofing and doors with steel, employing security personnel, installing intrusion detection systems
  2. The room should be installed with a gaseous fire extinguisher, smoke detectors
  3. power surges and brownouts should be avoided by maintaining a stable power supply by use of an Uninterruptible Power Supply(UPS).
  4. The room should be well laid out. Power and data cables should be kept off the user paths to avoid stumbling on them.
  5. Computers should be protected from dust by covering them while not in use and fitting the windows with curtains.
  6. Drinks and solid food should be avoided in the computer laboratory. Drinks with water content may cause corrosion of metallic parts of a computer. Food particles may clog the movable computer parts causing malfunctioning.
  7. Dehumidifiers should be used to control dampness

Hands-on Skills Lesson I

By the end of this lesson, you should be able to: Define booting Differentiate between cold and warm booting Describe the booting process Demonstrate the starting of a computer Demonstrate the steps of shutting down a computer

Booting a computer

Booting refers to the overall processing of making a computer ready for use

Types of Booting

  1. Cold booting
  2. Warm Booting

Cold Booting

This refers to starting a computer that was off initially by pressing the power button

Warm Booting

This refers to the processes of restarting that was initially on by clicking on the restart button

Booting process

Once the computer is turn on, the BIOS checks the input and output hardware if they are in a good. This is known as Power On Self Test.If there is no problem encountered during this process, the Operating System is loaded onto the RAM and takes over the control of the computer. Note that during the booting process the computer also reads the correct time from the CMOS memory. If the battery for the CMOS memory has worn out, the computer prompts the user to enter the current date and time every time a the computer starts.

Shutting down a computer

If the Operating system is windows 10.

  1. Step 1: Close all the running programs
  2. Step 2:Point to the start button and click once to display the start menu.
  3. Step 3:On the start menu, click on the power button, this displays sleep, shutdown and Restart Options
  4. Step 4: Click on the shutdown option to shutdown the computer

Hands-on Skills Lesson II

By the end of the lesson, you should be able to: state and explain various categories of keys on a computer keyboard Give examples of the above categories type while observing the typing guidelines

Keyboarding Skills

Categories of keys on a computer keyboard

Typing(Alphanumeric) keys

These are A-Z and 0-9

Function Keys

These are F1-F12

Cursor movement Keys

  • Arrow keys
  • Page up and down keys
  • Home and end keys

Editing Keys

  • delete
  • insert

Special purpose keys

Used together with other keys to issue specific commands to a computer

They include:

  • Shift
  • Control(ctrl)
  • Alt
  • Escape(Esc)

Numeric keypad keys

They are used when Num Lock is turned on

0-9 and arithmetic keys

Typing Guidelines

  1. Sit upright with both feet firm on the ground maintaining a straight upward posture
  2. Place the material to be typed on the left handside at an accessible distance to avoid eyestrain
  3. Rest both hands on the keyboard with fingers resting on the home keys.
  4. Always take your fingers back to home keys after striking other keys
  5. Never look at  your fingers while typing so you may improve on typing speed

Left hand home keys

  • A.,S,D,F

Right hand home keys

  • JKL and ;

Hands-on Skills Lesson III

By the end the lesson you should be able to : Perform the four mouse operations Define the four mouse operation terminologies  

Mouse Skills

Guidelines for using a mouse

  1. The mouse should be placed on a flat smooth surface
  2. use the thumb and two fingers to hold the mouse, the middle finger should rest on the right button, the index finger on the left button, and the thumb on the side.

Common Mouse Operations

Clicking - Pressing and releasing the left mouse button once. This operation is used to execute commands and select icons

Double-clicking: Pressing and release the left button of the mouse twice in quick succession.  This operation is used to open a folder or a file or to launch an application

Right-Clicking - This refers to pressing and releasing the right button of the mouse once. This operation is used to display a context menu.

Drag and Drop - It is where the user points to an icon, hold down the left button of the mouse and drags the icon to the next location, and releases the button.


By Donald Trung Quoc Don, Computer Mouse