In this lesson you will learn about computer hardware and its working. Hardware includes any device that is connected to your computer and is controlled by your computer’s microprocessor. This includes equipment that was connected to your computer when it was manufactured, as well as peripheral equipment that you added later.

In this chapter, you will learn to:

  • Which devices are used to input data, to process data and to output processed data so we can use it.
  • What makes computers modular.
  • How computers can communicate .
  • What is the part of software.

Introducing Hardware

Computer hardware is the collection of physical elements that constitutes a computer system. Computer hardware refers to the physical parts or components of a computer such as the monitor, mouse, keyboard, computer data storage, hard drive disk (HDD), system unit (graphic cards, sound cards, memory, motherboard and chips), etc. all of which are physical objects that can be touched.

Components of Computer

A computer system consists of both hardware and information stored on hardware. Information stored on computer hardware is often called software.

  • The hardware components of a computer system are the electronic and mechanical parts.
  • The software components of a computer system are the data and the computer programs.

The Various component of a PC are:

System unit: Is a box-like structure that houses the necessary components to run the computer.

Keyboard: Is a component that closely resembles a typewriter.

Visual Display Unit (VDU): Is a component that resembles a TV screen. It is also called as a monitor.

Mouse: Is a tiny device connected to the system unit through a cord resembling a tail is called a mouse. Moving the mouse produce a corresponding movement of an arrowhead on the VDU.

Microphone: Is used to record sound in the computer.

Printer: Is used to print the result of any operation done on the computer.

Speakers: Are used to play sound applications on the computer.


Hardware Components

The major hardware components of a computer system are:  

  • Processor
  • Primary memory
  • Secondary memory
  • Input devices
  • Output devices


Understand CPU/Processor


CPU (Central Processing Unit)

  • CPU is considered as the brain of the computer.
  • CPU performs all types of data processing operations.
  • It stores data, intermediate results and instructions (program).
  • It controls the operations of all parts of computer.

CPU itself has the following three components

  • ALU (Arithmetic Logic Unit)
  • Memory Unit
  • Control Unit

Arithmetic Section

Function of Arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication and division. All complex operations are done by making repetitive use of above operations.


Logic Section

Function of logic section is to perform logic operations such as comparing, selecting, matching and merging of data.


Control Unit:

This unit controls the operations of all parts of computer. It does not carry out any actual data processing operations.

Functions of this unit are:

  • It is responsible for controlling the transfer of data and instructions among other units of a computer.
  • It manages and coordinates all the units of the computer.
  • It obtains the instructions from the memory, interprets them and directs the operation of the computer.
  • It communicates with Input/output devices for transfer of data or results from storage.
  • It does not process or store data.


Memory or Storage Unit:

This unit can store instructions, data and intermediate results. This unit supplies information to the other units of the computer when needed. It is also known as internal storage unit or main memory or primary storage or Random access memory (RAM).

Its size affects speed, power and capability. There are primary memory and secondary memory, two types of memories in the computer. Functions of Memory Unit are:

  • It stores all the data to be processed and the instructions required for processing.
  • It stores intermediate results of processing.
  • It stores final results of processing before these results are released to an output device. All inputs and outputs are transmitted through main memory.



A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts. Each part is called cell. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if computer has 64k words, then this memory unit has 64 * 1024=65536 memory location. The address of these locations varies from 0 to 65535.


Memory is primarily of three types:

  • Cache Memory
  • Primary Memory/Main Memory
  • Secondary Memory

Cache Memory

Cache memory is a very high speed semiconductor memory, which can speed up CPU. It acts as a buffer between the CPU and main memory.

It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.


  • Cache memory is faster than main memory.
  • It consumes less access time as compared to main memory.
  • It stores the program that can be executed within a short period of time.
  • It stores data for temporary use.


  • Cache memory has limited capacity.
  • It is very expensive.


Primary Memory (Main Memory)

Primary memory is computer memory that a processor or computer accesses first or directly. It allows a processor to access running execution applications and services that are temporarily stored in a specific memory location. Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data gets lost when power is switched off. Primary memory is also known as primary storage or main memory

It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instructions required to be processed earlier reside in main memory. It is divided into two subcategories RAM and ROM.

  • Characteristic of Main Memory These are semiconductor memories.
  • Usually volatile memory.
  • Data is lost in case power is switched off.
  • It is working memory of the computer.
  • Faster than secondary memories.
  • A computer cannot run without primary memory.



Types of RAM

RAM is of two types:

  • Static RAM (SRAM)
  • Dynamic RAM (DRAM)


Static RAM (SRAM)

The word static indicates that the memory retains its contents as long as power remains applied.

However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.

Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher.

Static RAM is used as cache memory needs to be very fast and small.

Characteristics of the Static RAM:

  • It has long data lifetime
  • There is no need to refresh
  • Faster
  • Used as cache memory
  • Large size
  • Expensive
  • High power consumption

Dynamic RAM (DRAM)

DRAM, unlike SRAM, must be continually refreshed in order for it to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells. These cells are composed of one capacitor and one transistor.

Characteristics of the Dynamic RAM:

  • It has short data lifetime
  • Need to refresh continuously
  • Slower as compared to SRAM
  • Used as RAM
  • Lesser in size
  • Less expensive Less power consumption

Some other types of RAM

 EDO (Extended Data Output) RAM: In an EDO RAMs, any memory location can be accessed. Stores 256 bytes of data information into latches. The latches hold next 256 bytes of information so that in most programs, which are sequentially executed, the data are available without wait states.

SDRAM (Synchronous DRAMS): SGRAMs (Synchronous Graphic RAMs) These RAM chips use the same clock rate as CPU uses. They transfer data when the CPU expects them to be ready.

 DDR-SDRAM (Double Data Rate – SDRAM): This RAM transfers data on both edges of the clock.

Therefore the transfer rate of the data becomes doubles.


ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture.

A ROM stores such instructions as are required to start computer when electricity is first turned on, this operation is referred to as bootstrap. ROM chip are not only used in the computer but also in other electronic items like washing machine and microwave oven.

Following are the various types of ROM:

MROM (Masked ROM): The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kinds of ROMs are known as masked ROMs. It is inexpensive ROM. PROM (Programmable Read only Memory)

PROM (Programmable Read Only Memory): It is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM programmer. Inside the PROM chip, there are small fuses, which are burnt open during programming. It can be programmed only once and is not erasable.

EPROM (Erasable and Programmable Read Only Memory): The EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser achieves this function. During programming, an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is passed through a quartz crystal window (lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.


EEPROM (Electrically Erasable and Programmable Read Only Memory): The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 MS (millisecond). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of re-programming is flexible but slow.


Advantages of ROM

  • Non-volatile in nature
  • These cannot be accidentally changed
  • Cheaper than RAMs
  • Easy to test
  • More Reliable than RAMs
  • These are static and do not require refreshing
  • Its contents are always known and can be verified

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing Data/Information permanently.

CPU directly does not access these memories, instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory and then CPU can access it. For example, HD disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory

  • These are magnetic and optical memories.
  • It is known as backup memory.
  • It is non-volatile memory.
  • Data is permanently stored even if power is switched off.
  • It is used for storage of the data in the computer.
  • Computer may run without secondary memory. Slower than primary memories.

Optical Disks: Optical disk is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. There are three basic types of optical disks: Read-only optical disks, Write once read many Optical disks and Rewritable Optical disks. Two main types of optical disks are:

  1. CD – is an abbreviation of compact disk, and is a form of data storage that can transfer data up to the speed of 7800 KB/s. A standard 120 mm CD holds up to 700 MB of data, or about 70 minutes of audio.
  2. DVD: is an abbreviation of Digital Versatile Disc, and is an optical disc storage media format that can be used for data storage. The DVD supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps.


Flash Drive: A flash drive is a small external storage device, typically the size of a human thumb that consists of flash memory. USB flash drives are removable and rewritable reads and writes to flash memory. They are a solid-state storage medium that’s both inexpensive and durable.

Flash Memory cards: Flash memory is an EEPROM non-volatile computer storage chip. These Memory cards currently vary in sizes between 1 Gigabytes -16 Gigabytes and they transfer data at a rate of approximately 14.65 MB/s.


Input Devices

In computing, an input device is any peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system such as a computer or other information appliance. Examples of input devices include keyboards, mouse, light pen and joysticks.

Keyboard: Most common and very popular input device is keyboard. The keyboard helps in inputting the data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing some additional functions. Keyboards are of two sizes 84 keys or 101/102 keys, but now 104 keys or 108 keys keyboard is also available for Windows and Internet.

Mouse: Mouse is most popular Pointing device. It is a very famous cursor-control device. It is a small palm size box with a round ball at its base which senses the movement of mouse and sends corresponding signals to CPU on pressing the buttons. Generally, it has two buttons called left and right button and scroll bar is present at the mid. Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text into the computer. Advantages:

  • Easy to use
  • Not very expensive
  • Moves the cursor faster than the arrow keys of keyboard.

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

Light Pen: Light pen is a pointing device, which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube.

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.

Scanner: Scanner is an input device, which works more like 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.


Output Devices

An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) which converts the electronically generated information into human-readable form. Display devices

VDU (video display unit):is the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. The sharpness of the image depends upon the number of the pixels.

There are two kinds of viewing screen used for monitors:

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

Cathode-Ray Tube (CRT) Monitor: In the CRT, display is made up of small picture elements called pixels for short. The smaller the pixels, the better the image clarity or resolution. It takes more than one illuminated pixel to form whole character, such as the letter ‘e’ in the word help. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. There are some disadvantages of CRT:

  • Large in Size
  • High power consumption


Flat-Panel Display Monitor: The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement compared to the CRT. You can hang them on walls or wear them on your wrists. Current uses for flat-panel displays include calculators, video games, monitors, laptop computer, graphics display.  

The flat-panel display are divided into two categories:

  • Emissive Displays – The emissive displays are devices that convert electrical energy into light. Example are plasma panel and LED (Light-Emitting Diodes).
  • 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)


Speaker: A hardware device connected to a computer’s sound card that outputs sounds generated by the computer.



Printers: Printer is the most important 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 the ribbon and onto the paper, are called impact printers.

Characteristics of Impact Printers are the following:

  • Very low consumable costs
  • Impact printers are very noisy
  • Useful for bulk printing due to low cost
  • There is physical contact with the paper to produce an image

These printers are of two types:

  • Character printers
  • Line printers

Character Printers: Character Printers are printers, which print one character at a time. These are of further two types:

  • Dot Matrix Printer (DMP)
  • Daisy Wheel

Dot Matrix Printer: In the market, one of the most popular printer is Dot Matrix Printer because of their ease of printing features and economical price. Each character printed is in form of pattern of Dot’s and head consists of a Matrix of Pins of size(5*7, 7*9, 9*7 or 9*9) which comes out to form a character that is why it is called Dot Matrix Printer.


  • Inexpensive
  • Widely Used
  • Other language characters can be printed


  • Slow Speed
  • Poor Quality



Daisy Wheel: Head is lying on a wheel and Pins corresponding to characters are like petals of Daisy (flower name) that is why it is called Daisy Wheel Printer. These printers are generally used for word processing in offices which require a few letters to be sent here and there with very nice quality representation.


  • More reliable than DMP’s
  • Better quality
  • The fonts of character can be easily changed.


  • Slower than DMP’s
  • Noisy
  • More expensive than DMP’s

Line Printers: Line printers are printers, which print one line at a time.


These are of further two types:

  • Drum Printer
  • Chain Printer

Drum Printer: This printer is like a drum in shape so it called drum printer. The surface of drum is divided into 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 prints one line. Drum Printers are fast in speed and prints between 300 to 2000 lines per minute.


  • Very high speed


  • Very expensive
  • Characters fonts cannot be changed.


Chain Printer: In this printer, chain of character sets are used so it called Chain Printers. A standard character set may have 48, 64, 96 characters.


  • Character fonts can easily be changed.
  • Different languages can be used with the same printer.


  • Noisy
  • Do not have the ability to print any shape of characters.

Non-impact Printers: The printers that print the characters without striking against the ribbon and onto the paper are called Non-impact Printers. These printers print a complete page at a time, also called as Page Printers.

These printers are of two types:

  • Laser Printers
  • Inkjet Printers

Characteristics of Non-impact Printers:

  • Faster than impact printers.
  • They are not noisy.
  • High quality.
  • Support many fonts and different character size.

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.


  • Very high speed.
  • Very high quality output.
  • Gives good graphics quality.
  • Supports many fonts and different character sizes.


  • Cannot be used to produce multiple copies of a document in a single printing.

Inkjet Printers: Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.

They make less noise because no hammering is done and these have many styles of printing modes available. Color printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also.


  • High quality printing
  • More reliable


  • Expensive as cost per page is high
  • Slow as compared to laser printer




The motherboard serves as a single platform to connect all of the parts of a computer together. A motherboard connects CPU, memory, hard drives, optical drives, video card, sound card and other ports and expansion cards directly or via cables. It can be considered as the backbone of a computer. Some popular manufacturers are Intel, ASUS, AOPEN, ABIT, and BIOSTAR.


  • Motherboard varies greatly in supporting various types of components.
  • Normally, a motherboard supports a single type of CPU and few types of memories.
  • Video Cards, Hard disks, Sound Cards have to be compatible with motherboard to function properly.
  • Motherboards, cases and power supplies must be compatible to work properly together.


 Computer-Memory Unit

  • It is the amount of data that can be stored in the storage unit. The storage capacity are expressed in terms of Bytes.

Following are the main memory storage units:

Sr. No. Unit Description
1 Bit (Binary Digit) A binary digit is logical 0 & 1 representing a passive or an active state of a component in an electric circuit.
2 Nibble A group of 4 bits is called nibble.
3 Byte A group of 8 bits is called byte. A byte is the smallest unit, which can represent a data item or a character.
4 Word A computer word like a byte, is a group of fixed number of bits processed as a unit which varies from computer to computer but is fixed for each computer.

The length of a computer word is called word-size or word length and it

may be as small as 8 bits or may be as long as 96 bits.

A computer stores the information in the form of the computer words.

Few higher storage units are the following:





Kilobyte (KB)
Megabyte (MB)
Gigabyte (GB)
Terabyte (TB)
Petabyte (PB)

1 KB = 1024 Bytes
1 MB = 1024 KB
1 GB = 1024 MB
1 TB = 1024 GB
1 PB = 1024 TB



Software is a set of programs, which are designed to perform a well-defined function. A program is a sequence of instructions written to solve a particular problem.

There are three types of software’s:

  • System Software
  • Application Software
  • Utility Software


System Software

The system software is a collection of programs designed to operate, control and extend the processing capabilities of the computer itself. System software are generally prepared by computer manufacturers.

These software’s comprise of programs written in low level languages which interact with the hardware at a very basic level. System software serves as the interface between hardware and the end users.

Some examples of system software are Operating System, Compilers, Interpreter, Assemblers, etc.


Features of System Software are the following:

  • Close to system.
  • Fast in speed.
  • Difficult to design.
  • Difficult to understand.
  • Less interactive.
  • Smaller in size.
  • Difficult to manipulate.
  • Generally written in low-level language.

Application Software

  Application software’s are the software’s that are designed to satisfy a particular need of a particular environment. All software’s prepared by us in the computer lab can come under the category of Application Software.

Application software may consist of a single program, such as a Microsoft’s notepad for writing and editing simple text. It may also consist of a collection of programs, often called a software package, which work together to accomplish a task, such as a spreadsheet package.

Examples of Application software’s are the following:

  • Payroll Software
  • Student Record Software
  • Inventory Management Software
  • Income Tax Software
  • Railways Reservation Software
  • Microsoft Office Suite Software
  • Microsoft Word
  • Microsoft Excel
  • Microsoft PowerPoint

Features of Application Software are the following:

  • It is close to user.
  • It is easy to design.
  • More interactive.
  • Slow in speed.
  • Generally written in high-level language.
  • Easy to understand.
  • Easy to manipulate and use.
  • Bigger in size and requires large storage space.


Utility Software

Utility software is system software designed to help analyze, configure, optimize or maintain a computer.

Utility software usually focuses on how the computer infrastructure (including the computer hardware, operating system, software and data storage) operates.

Some of utility software are as follow:- Anti-virus: utilities scan for computer viruses

Disk checkers: can scan operating hard drive

Memory testers: check for memory failures.