Chapter 2 – Components of Computer System


Any computer system consists of the four basic units; namely input unit, storage unit, central processing unit and output unit. Central Processing unit consists of Arithmetic logic unit and Control unit. A computer performs five major functions no matter what size they are of as follows:

  • Data or Instructions are accepted as input,
  • Data and Instruction are stored
  • Processing of data as per the instructions,
  • Control of all operations inside the computer
  • Result  in the form of output.
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Basic Components of Computer Systems

Following are the various components of a computer system–

Input Unit

Data and instructions must enter the computer system before any computation can be performed on the supplied data. The input unit that links the external environment with the computer system performs this task. An input unit performs the following functions :

  • It accepts (or reads) the list of instructions and data from the outside world.
  • It converts these instructions and data in computer acceptable format.
  • It supplies the converted instructions and data to the computer system for further processing.

Output Unit

The job of an output unit is just the reverse of that of an input unit. It supplied information and results of computation to the outside world. Thus it links the computer with the external environment. As computers Chapter 2 Components of Computer System work with binary code, the results produced are also in the binary form. Hence, before supplying the results to the outside world, it must be converted to human acceptable (readable) form. This task is accomplished by units called output interfaces. Following functions are performed by an output unit.

  • It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us.
  • It converts these coded results to human acceptable (readable) form.
  • It supplied the converted results to the outside world.

Storage Unit

The data and instructions that are entered into the computer system through input units have to be stored inside the computer before the actual processing starts. Similarly, the results produced by the computer after processing must also be kept somewhere inside the computer system before being passed on to the output units. The Storage Unit or the primary / main storage of a computer system is designed to do all these things. It provides space for storing data and instructions, space for intermediate results and also space for the final results.

The specific functions of the storage unit are to store:

  • All the data to be processed and the instruction required for processing (received from input devices).
  • Final results of processing before these results are released to an output device.
Central processing unit (Cpu)

Central Processing Unit

The main unit inside the computer is the CPU. This unit is responsible for all events inside the computer. It controls all internal and external devices, performs “Arithmetic and Logical operations”. The operations a Microprocessor performs are called “instruction set” of this processor. The instruction set is “hard wired” in the CPU and determines the machine language for the CPU. The more complicated the instruction set is, the slower the CPU works. Processors differed from one another by the instruction set. If the same program can run on two different computer brands they are said to be compatible. Programs written for IBM compatible computers will not run on Apple computers because these two architectures are not compatible. The control Unit and the Arithmetic and Logic unit of a computer system are jointly known as the Central Processing Unit (CPU). The CPU is the brain of any computer system. In a human body, all major decisions are taken by the brain and the other parts of the body function as directed by the brain. Similarly, in a computer system, all major calculations and comparisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system.

Arithmetic and Logic Unit (ALU)

The Arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of the instructions take place during the processing operations. All calculations are performed and all comparisons (decisions) are made in the ALU. The data and instructions, stored in the primary storage prior to processing are transferred as and when needed to the ALU where processing takes place. No processing is done in the primary storage unit. Intermediate results generated in the ALU are temporarily transferred back to the primary storage until needed at a later time. Data may thus move from primary storage to ALU and back again as storage many times before the processing is over. After the completion of processing, the final results which are stored in the storage unit are released to an output device.

The arithmetic and logic unit (ALU) is the part where actual computations take place. It consists of circuits that perform arithmetic operations (e.g. addition, subtraction, multiplication, division over data received from memory and capable to compare numbers (less than, equal to, or greater than).

Control Unit

The control unit directs and controls the activities of the internal and external devices. It interprets the instructions fetched into the computer,determines what data, if any, are  needed, where it is stored, where to store the results of the operation, and sends the control signals to the devices involved in the execution of the instructions.

Register : In a computer, a register is one of a small set of data holding places that are part of a computer processor. A register may hold a computer instruction, a storage address, or any kind of data (such as a bit sequence or individual characters).
Input Devices

Input devices include those devices with the help of which we enter data into computer as they  make a link between user and computer. These devices translate the human readable information into the form understandable by computer. The various devices are as follows –

1. Keyboard : Keyboard is among the most common and popular input device . It is used to  input the data to the computer. In traditional times the type writer was used. The keyboard has the layout similar to that of a type writer but some additional keys are present that have additional functions.

The keys are following :

Keys Description
Typing Keys These keys include the letter keys (A-Z) and digits keys (0-9).
Numeric Keypad It is used to enter numeric data or cursor movement. It has a set of 17 keys that are in the same layout as that of calculators.
Function Keys There are twelve functions keys present on the keyboard. These are arranged in a row along the top of the keyboard. Each function key has unique meaning and is used for some specific purpose.
Controls Keys These keys are used to provide cursor and screen control. It includes four directional arrow key. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
Special Purpose Keys Keyboard also contains some special purpose keys such as Enter,Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.

2. Mouse : Mouse  is a cursor-control device . It is a pointing and drop device. It’s size is good enough to fit the palm. It has a  palm size box with a round ball at its base. It  senses the movement of mouse and sends corresponding signals to CPU on pressing of the  buttons. There are two buttons that provide the left  click and the right click. A scroll bar is present in the mid. Mouse is only used to control the position of cursor on screen.

3. Joystick : Just like the mouse , Joystick is also a pointing device, which is used to move cursor position on a monitor screen. It has a stick that has a  spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in  four directions. It is mainly used in Computer Aided Designing (CAD) and playing computer games.

4. Light Pen : Light pen is also a pointing device. Its structure is similar to that of a  pen. It is based on an optical system placed in a small tube. It is used to  select a displayed menu item or draw pictures on the monitor screen. When light pen’s tip is moved over the monitor screen and pen button is pressed, its photocell sensing element, detects the screen location and sends the corresponding signal to the CPU

5. Track Ball : Track ball are used mostly in notebook or laptop computer. This is a ball, which is half inserted and by moving fingers on ball, pointer can be moved. Atrack ball requires less space than a mouse  as the whole device is not moved. A track ball can come in various shapes like a ball, a button and a square.

6. Scanner : Scanner is an input device, which works on a similar principle of a  photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disc of the computer for further manipulation. Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed.

7. Touch Screen : A touchscreen is an electronic visual display that the user can control through simple or multi-touch gestures by touching the screen with a special stylus/pen and-or one or more fingers. Some touch screens use an ordinary or specially coated gloves to work while others use a special stylus/pen only. The user can use the touchscreen to react to what is displayed and to control how it is displayed (for example by zooming  the text size).

8. Digitizer : Digitizer is an input device which converts analog signal from the television camera  into a strings of binary digits that can be stored in a computer. It converts the analog information into a digital form. Digitizer is also known as Tablet or Graphics tablet. They can be used by the computer to create a picture of whatever the camera had been pointed at.

9. Magnetic Ink Card Reader (MICR) : We see in banks, libraries etc using MICR as an input device . As large number of cheques are processed everyday MICR serves a very useful purpose. A special type of ink that contains particles of magnetic material that is machine readable, is used to read the  code number and cheque number that are printed on the cheques in banks. This reading process is called Magnetic Ink Character Recognition (MICR). The main advantage of MICR is that it is highly accurate and fast in reading.

10. Optical Character Reader (OCR) : OCR is an input device that is used to read a printed text. The role of OCR  is to scan the text optically character by character by converting them into a machine readable code and store the text on the system. The OCR is used for the preparation of electricity bills, insurance premium, telephone bills.

11. OMR (Optical Mark Recognition) : Optical mark recognition (also called optical mark reading and OMR) is the process of capturing human-marked data from document forms such as surveys and test.

12. SCR (Smart Card Readers) : A small electronic device about the size of a credit card that contains electronic memory, and possibly an embedded  integrated circuit (IC). Smart cards containing an IC are sometimes called Integrated Circuit Cards (ICCs).

Smart cards are used for a variety of purposes, including:

  • Storing a patient’s medical records
  • Storing digital cash
  • Generating network IDs (similar to a token)

To use a smart card, either to pull information from it or add data to it, you need a smart card reader, a small device into which you insert the smart card.

13. Bar Code Readers : Bar Code Reader is a device used for reading bar coded data (data in form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc. Bar Code Reader scans a bar code image by converting it into an alphanumeric values . This value is then fed to the computer to which bar code reader is connected.

14. Microphone : A microphone,is an acoustic-to-electric transducer or sensor that converts sound in air into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, two-way radios, megaphones, radio and television broadcasting, and in computers for recording voice, speech recognition, VoIP,and for non-acoustic purposes such as ultrasonic checking or knock sensors.

15. Webcam : A webcam is a video camera that feeds or streams its image in real time to or through a computer to computer network. When “captured”  by the computer, the video stream may be saved, viewed or sent on to other networks via systems such as the internet, and email as an attachment. When sent to a remote location, the video stream may be saved, viewed or on sent there. Unlike an IP camera (which connects using Ethernet or Wi-Fi), a webcam is generally connected by a USB cable, or similar cable, or built into computer hardware, such as laptops.

Output Devices

An output device is that component of computer hardware that communicates the results of data that is processed by the computer  and converts the digital   information into a form easily read and understood by humans. Various Output devices are used in Computers.

1.  Monitors : Monitor or the Visual Display Unit (VDU) is the main output device of a computer. It forms images in the form of  tiny dots, known as pixels. The sharpness of the image can be determined by the number of the pixels.

Two kinds of viewing screens are used for monitors:

  • Cathode-Ray Tube (CRT)
  • Flat-Panel Display

(a) Cathode-Ray Tube (CRT) Monitor :

In the CRT,display consists of  small picture elements known as  pixels and determine the resolution of the image. Smaller are the pixels the better is  the image clarity or resolution. Finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes that serve as a fixed location on the screen where a standard character can be placed.Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. However the CRT has some disadvantages as it is large in Size and has a high power consumption.

(b) Flat-Panel Display Monitor : 

These flat panel displays overcome the disadvantages of CRT as they have reduced volume, weight and power requirement compared to the CRT. They come in different shapes and size. You can hang them on walls or wear them on your wrists. They are used in all modern day  calculators, video games, monitors, laptop computer, graphics display etc as displays. The at-panel display are of two main types :

  1. Emissive Displays : The emissive displays convert electrical energy into light.  Example are plasma panel and LED (Light-Emitting Diodes).
  2. Non-Emissive Displays : The Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. Example is LCD (Liquid-Crystal Device)

(c) 3-D Monitors:

It is a television that conveys depth perception to the viewer. 3-D describes an image that provides the perception of length. When 3-D images are made interactive then user feel involved with the scene and this experience is called virtual reality.

2. Printers :  Printer is among the most common output device, which is used to print information on paper.

There are two types of printers:

  • Impact Printers
  • Non-Impact Printers

Impact Printers :

The printers that print the characters by striking against a ribbon and then onto the paper, are called impact printers.

Impact Printers are low of cost but they happen to be very noisy. Due to their low cost they are useful for bulk printing. There is physical contact with the paper to produce an image.

Impact printers can be further divided into two types:

(i) Character printers :

These printers print one character at a time. These further divided into two such as the Dot Matrix Printer and the daisy wheel printer.

Dot matrix printer:

They are the most popular printers because of their ease of printing features. They come at a low cost. Each character is printed in the form of pattern of Dot’s and head .These dots and heads consist of a matrix of pins of size (5 * 7, 7 * 9, 9 * 7 or 9 * 9) that result in forming a character. Hence they are called as Dot Matrix Printer.

Daisy Wheel:

These are known as daisy wheel printers as the head lies on the wheel and Pins correspond to characters  like petals of Daisy flower. These printers are  used for word-processing in offices and offer  very nice quality representation.

(ii) Line Printers : 

Line printers are printers, which print one line at a time. Speed of line printers is limited by the speed of cartridge used. These can be divided into two types: The drum printer and the Chain printer

Drum Printer :

This printer looks like  a drum in shape that’s why it is called a drum printer. The Drum surface has a number of tracks. Total tracks are equal to size of paper, i.e., for a paper width of 132 characters, Drum will have 132 tracks. A character set is embossed on track. The different character sets available in market are 48 character set, 64 and 96 characters set. One rotation of drum leads to printing of  one line. These printers  print between 300 to 2000 lines per minute. Hence they have a very high speed.

Chain Printer :

In this printer because chain of character sets are used hence they are called as Chain Printers. A standard character set may have 48, 64, 96 characters.

Non-impact Printers :

These printers  print the characters without the physical contact with the paper i.e  without striking against the ribbon and onto the paper. These printers print one complete page at a time, and are also called as Page Printers.

These printers are of two types:

Laser Printers and the Ink-jet Printers.

(i) Laser Printers : These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.

(ii) Inkjet Printers : Ink-jet printers are new technology non-impact character printers. They print characters via spraying small drops of ink onto paper. Ink-jet printers produce very high quality output with presentable features. They are noiseless printers and have many styles of printing modes available. These are also called as the coloured printers. Models of Ink-jet printers can produce multiple copies of printing also.

3. Headphones : Headphones are referred to as earphones, headphones are a hardware device that either plugs into your computer (line out) or your speakers  and allow you to privately listen to audio without disturbing anyone else. The picture is an example of a USB headset from Logitech with a microphone and a popular solution for computer gaming.

4. Speaker : A hardware device connected to a computer’s sound card that outputs sounds generated by the computer. It needs a sound card connected to a CPU, that generates sound via a card. These are used for listening music, for being audible in seminars etc.

5. Projector : A projector is an output device that can take images generated by a computer and reproduce them on a large, flat (usually lightly colored) surface. For example, projectors are used in meetings to help ensure that all participants can view the information being presented.

Some important points –

  • External devices such as printers key boards and modems are known as peripherals.
  • The higher the resolution of a monitor the closer together the pixels.
  • The rate at which scanning is repeated in a CRT is called refresh rate best position for
  • Tail towards the user is the best position for operating the mouse.
Maintaining Computer Systems

We must ensure that the computer is well looked after. It can only run smoothly if it is protected valuable from malicious viruses which can wreak havoc on your PC or Mac.

Computers that become overloaded or vulnerable to viruses can  freeze or crash. This can lead to loss of information. Hackers who hack professionally can be a threat to the computers. There are some extremely sophisticated and technologically advanced group or individuals who are hackers and can destabilise operating systems and bring computer networks crashing down.

This can lead to a slow computer. Each time a web page is opened or an attachment is downloaded  certain data on the computer gets collected, much of it is not needed to be used again. This data gets clogged up on your hard drive and can affect your computer’s performance if you don’t do a spring clean once. Your computer must be given a general assessment every couple of months. A general assessment  should be done more frequently (around once a month) if your computer is used a lot.

Backing Up

It is a very important thing to get into the habit of backing up your files on a regular basis. This means having a recent copy of important data held onto your computer. The important documents on your system include the invoices, legal documents or personal files such as photo albums.

You can copy your files to a USB memory stick. USB memory stick do not have enough data to store. They can be quite expensive to buy. They have been popular because of their portability as they’re easy to use.

Disk imaging is one of the most effective methods of backing up. This is a more expensive method as it is the most fail-safe method of restoring everything on your computer if you lose everything on your hard drive. With the advent of various online backup you can enlist to help with the storage of your computer’s data, which are incredibly convenient as the backup is done automatically and your files are kept in a safe online environment that you can access at any time.

Deleting files

Storing huge data and big files on your computer can bring performance speeds immediately down. In order to make sure your computer is running efficiently it’s important to delete unnecessary files from time to time. Windows operating systems has a disk cleanup function that is extremely quick and easy to use. Disk cleanup doesn’t take too long to run. This utility on your computer cleans up all the unwanted files that are stored in your computer’s cache.

Scanning your hard drive

It is really important to Scan your hard drive as an another routine task which you should get into the habit of doing regularly. This utility examines the hard drive for some errors that could have a direct affect on your computer’s efficiency. This needs to be done around once a week to use your computer every day or once in a month incase if you use it less frequently.

Defragmenting your hard drive

The computer’s hard drive can become clogged up with numerous files that are broken up across various locations around the drive. The drive becomes really chaotic. Due to the drive getting chaotic  your computer gradually slow’s down in its speed as it tries to access information from files scattered all over the drive. Hence it’s really important to carry out a process that rationalises the various files from time to time.

Defragmentation collects all the different parts of one file back together in one place in the hard drive. Then it in turns reorganizes information and places the files that are used most frequently. Defragmention process leads to a much faster running computer.

Clearing your cache (cookies and Internet files)

This folder cache is of temporary Internet files folder that is a record of files which have been viewed or downloaded from the web, including web pages, images, music and cookies (small files that websites can create on your computer to help them deliver personalised content when you next visit.

Automatic updating

Computer hackers are determined to destabilise computer software through their malicious programs.  A number of big companies like Microsoft , ‘patch’their products in order to ensure their safety. If you run on windows then make sure your computer is set to update automatically. These updates can be automated by clicking on the start then programs. Windows updates ensure that you’re set to install updates automatically.

Checking for viruses

Installing some form of anti-virus software is a must. The computer is  vulnerable to a range of viruses. These viruses are transmitted to your computer via infected email attachments. These viruses are called as worms and can spread over the Internet. The viruses are used by criminals in order to gather personal information. These worms can have serious consequences. Viruses have the capability of gathering financial information and secret data such as passwords and user names.

Hence making adequate arrangements of prevention is always better than cure.Installing enough anti virus protection programs for virus protection on your computers is the best way to protect your computer.

Anti-virus software can be bought as stand-alone or as a  comprehensive security suite. Example of various software manufacturers include McAfee  and AVG.

Installing anti-malware, spyware and adware

Malware, spyware and adware all pose a significant threat to your online privacy and the smooth-running of your computer. It is extremely essential to install along with anti-virus software , the anti spyware software also. The spyware can spy on your online activities, as it installs unwanted program on your computer. Adware is used by commercial companies to find out more about consumers and track the effectiveness of their advertising, but it can have more dire consequences. Malicious adware or spyware is very hard to remove from your computer. It can cause to block access to certain websites, stop you running anti virus software, scan your hard disk and locate sensitive personal information, such as credit card numbers and other personal information which can then be used for criminal activities.

In order to ensure that you don’t fall victim you can install an anti-spyware software. They work in the same way as anti-virus software. These free Downloadable products include Ad-Aware and Microsoft Defender.  As with anti-virus software, the free versions may not be quite as comprehensive as their paid for counterparts but they should provide a decent level of protection.

Setup a Firewall

Firewalls are a significant way of protecting your  computer from some of the threats that have crept up in the cyberspace world. Firewalls are an effective way to safeguard you from hackers, viruses and worms. These viruses can endanger the personal information that is kept on your computer. Firewalls are a barrier between your computer and the world outside. But firewalls are not enough to be relied on only. They alone cannot protect your computer from online threats. Your firewall should be used in conjunction with other forms of computer security, such as your anti-virus software.

Windows packages contain a ‘desktop firewall’, for which you don’t need to pay for and provide a basic level of security. The broadband internet router that is used for an internet connection also a firewall built into it, which can be controlled via your computer and which is password protected.

Cleaning your computer

Ensuring that your computer is clean of dust and dirt can make sure that your computer is kept under hygienic conditions.  Make sure your computer is turned off and unplugged before you clean it.  You can buy specialist computer cleaning products or use a damp, lint-free soft cloth to gently dislodge dirt from the keyboard or the exterior of the computer.  A computer mouse is particularly susceptible to dirt, making it difficult to control.  To clean your mouse turn the retaining ring on the bottom of the mouse anti-clockwise to remove the mouse ball.  You can then use a clean soft cloth to remove any dust or dirt from inside the mouse.

It’s important to deal with any spillages on your keyboard quickly. Turn off your computer and then turn the keyboard on its side to drain off the excess. Use a soft cloth to mop up any remaining liquid and then let your keyboard dry off before using it again.