CS5: Computer Hardware

This unit explains the computer hardware

Input Devices

Following are some of the important input devices which are used in a computer −

  • Keyboard
  • Mouse
  • Joy Stick
  • Light pen
  • Track Ball
  • Scanner
  • Graphic Tablet
  • Microphone
  • Magnetic Ink Card Reader(MICR)
  • Optical Character Reader(OCR)
  • Bar Code Reader
  • Optical Mark Reader(OMR)


Keyboard is the most common and very popular input device which helps to input data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.

Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.

The keys on the keyboard are as follows −

Keys & Description

Typing Keys

These keys include the letter keys (A-Z) and digit keys (09) which generally give the same layout as that of typewriters.

Numeric Keypad

It is used to enter the numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.

Function Keys

The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has a unique meaning and is used for some specific purpose.

Control keys

These keys provide cursor and screen control. It includes four directional arrow keys. 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.


Mouse is the most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base, which senses the movement of the mouse and sends corresponding signals to the CPU when the mouse buttons are pressed.

Generally, it has two buttons called the left and the right button and a wheel is present between the buttons. A mouse can be used to control the position of the cursor on the screen, but it cannot be used to enter text into the computer.


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


Joystick is also a pointing device, which is used to move the 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 the 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 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 the tip of a light pen is moved over the monitor screen and the pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.

Track Ball

Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the pointer can be moved.

Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button, or a square.


Scanner is an input device, which works more like a photocopy machine. It is used when some information is available on paper and it is to be transferred to the hard disk of the computer for further manipulation.

Scanner captures images from the source which are then converted into a digital form that can be stored on the disk. These images can be edited before they are printed.


Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at.

Digitizer is also known as Tablet or Graphics Tablet as it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for fine works of drawing and image manipulation applications.


Microphone is an input device to input sound that is then stored in a digital form.

The microphone is used for various applications such as adding sound to a multimedia presentation or for mixing music.

Magnetic Ink Card Reader (MICR)

MICR input device is generally used in banks as there are large number of cheques to be processed every day. The bank’s code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable.

This reading process is called Magnetic Ink Character Recognition (MICR). The main advantage of MICR is that it is fast and less error prone.

Optical Character Reader (OCR)

OCR is an input device used to read a printed text.

OCR scans the text optically, character by character, converts them into a machine readable code, and stores the text on the system memory.

Bar Code Readers

Bar Code Reader is a device used for reading bar coded data (data in the form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc. It may be a handheld scanner or may be embedded in a stationary scanner.

Bar Code Reader scans a bar code image, converts it into an alphanumeric value, which is then fed to the computer that the bar code reader is connected to.

Optical Mark Reader (OMR)

OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked.

It is specially used for checking the answer sheets of examinations having multiple choice questions.


Output Devices

Following are some of the important output devices used in a computer.

  • Monitors
  • Graphics Plotter
  • Printer


Monitors, commonly called as Visual Display Unit (VDU), are 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 pixels.

There are two kinds of viewing screen used for monitors.

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

Cathode-Ray Tube (CRT) Monitor

The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity or resolution. It takes more than one illuminated pixel to form a whole character, such as the letter ‘e’ in the word help.

A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes – 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.

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 in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, and graphics display.

The flat-panel display is divided into two categories −

  • Emissive Displays− Emissive displays are devices that convert electrical energy into light. For example, plasma panel and LED (Light-Emitting Diodes).
  • Non-Emissive Displays− Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. For example, LCD (Liquid-Crystal Device).


Printer is an output device, which is used to print information on paper.

There are two types of printers −

  • Impact Printers
  • Non-Impact Printers

Impact Printers

Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper.

Characteristics of Impact Printers are the following −

  • Very low consumable costs
  • 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 the printers which print one character at a time.

These are further divided into two types:

  • Dot Matrix Printer(DMP)
  • Daisy Wheel

Dot Matrix Printer

In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in the form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character which 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) which is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices that require a few letters to be sent here and there with very nice quality.


  • More reliable than DMP
  • Better quality
  • Fonts of character can be easily changed


  • Slower than DMP
  • Noisy
  • More expensive than DMP

Line Printers

Line printers are the printers which print one line at a time.

These are of two types −

  • Drum Printer
  • Chain Printer

Drum Printer

This printer is like a drum in shape hence it is called drum printer. The surface of the drum is divided into a number of tracks. Total tracks are equal to the size of the paper, i.e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on the track. Different character sets available in the market are 48 character set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute.


  • Very high speed


  • Very expensive
  • Characters fonts cannot be changed

Chain Printer

In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.


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


  • Noisy

Non-impact Printers

Non-impact printers print the characters without using the ribbon. These printers print a complete page at a time, thus they are 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
  • Supports 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
  • Good graphics quality
  • Supports many fonts and different character size


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


Storage Devices

Alternatively referred to as digital storage, storage, storage media, or storage medium, a storage device is any hardware capable of holding information either temporarily or permanently. The picture shows an example of a Drobo, an external secondary storage device.

There are two types of storage devices used with computers: a primary storage device, such as RAM, and a secondary storage device, such as a hard drive. Secondary storage can be removable, internal, or external.

Examples of computer storage

Magnetic storage devices

Today, magnetic storage is one of the most common types of storage used with computers. This technology found mostly on extremely large HDDs or hybrid hard drives.

A hard drive

Floppy diskette

Hard drive

Magnetic strip


Tape cassette

Zip diskette

Optical storage devices

Another common storage is optical storage, which uses lasers and lights as its method of reading and writing data.

Blu-ray disc

CD-ROM disc

CD-R and CD-RW disc.

DVD-R, DVD+R, DVD-RW, and DVD+RW disc.

Flash memory devices

Flash memory has replaced most magnetic and optical media as it becomes cheaper because it is the more efficient and reliable solution.

USB flash drive, jump drive, or thumb drive.

CF (CompactFlash)

Memory card




SmartMedia Card

Sony Memory Stick

SD card


xD-Picture Card

Online and cloud

Storing data online and in cloud storage is becoming popular as people need to access their data from more than one device.

Cloud storage

Network media

Paper storage

Early computers had no method of using any of the above technologies for storing information and had to rely on paper. Today, these forms of storage are rarely used or found. In the picture to the right is an example of a woman entering data to a punch card using a punch card machine.


Punch card


A hard copy could be considered a form of paper storage that is still widely used although it cannot be easily used to input data back into a computer without the aid of OCR.

Why is storage needed in a computer?

Without a storage device, a computer cannot save or remember any settings or information and would be considered a dumb terminal.

Although a computer can run with no storage device, it would only be able to view information unless it was connected to another computer that had storage capabilities. Even a task such as browsing the Internet requires information to be stored on your computer.

Why so many different storage devices?

As computers advance, the technologies used to store data do too, right along with higher requirements for storage space. Because people need more and more space, want it faster, cheaper, and want to take it with them new technologies have to be invented. When new storage devices are designed, as people upgrade to those new devices the older devices are no longer needed and stop being used.

For example, when punch cards were first used in early computers, the magnetic media used for floppy disks was not available. After floppy diskettes had been released, they were replaced by CD-ROM drives, which were replaced by DVD drives, which have been replaced by flash drives. The first hard disk drive from IBM cost $50,000, was only 5 MB, big, and cumbersome. Today, we have smartphones that have hundreds of times the capacity at a much smaller price that we can carry with us in our pocket.

Each advancement of storage devices gives a computer the ability to store more data, as well as save and access data faster.

What is a storage location?

When saving anything on a computer, it may ask you for a storage location, which is the area where you would like to save the information. By default, most information is saved to your computer hard drive. If you want to move the information to another computer, save it to a removable storage device such as a flash drive.

Which storage devices are used today?

Most of the storage devices mentioned above are no longer used with today’s computers. Most computers today primarily use an SSD to store information and have the options for USB flash drives and access to cloud storage. Some desktop computers with disc drives use a disc drive that is capable of reading and writing CDs and DVDs.

What storage device has the largest capacity?

For most computers, the largest storage device is the hard drive or SSD. However, networked computers may also have access to larger storage with large tape drives, cloud computing, or NAS devices. Below is a list of storage devices from the smallest capacity to the largest capacity.


Many storage devices have been available in many different capacities. For example, over the evolution of the hard drive, there have been drives that range from the first hard drive of 5 MB to hard drives today that are several terabytes in size. Therefore, the below list is only meant to give a general understanding of the size differences between each storage devices today and is not an exact list. For example, the earliest hard drives are smaller than a CD.

Punch card

Floppy diskette

Zip disk



Blu-ray disc

Flash jump drive

Hard drive / SSD

Tape drive

NAS / Cloud Storage

Are storage devices input and output devices?

Although these devices do send and receive information, they are not considered an input device or output device. It is more proper to refer to any device capable of storing and reading information as a storage device, disk, disc, drive, or media.

How do you access storage devices?

Accessing a storage device on your computer depends on the operating system your computer is using and how it’s being used. For example, with Microsoft Windows, you can use a file manager to access the files on any storage device. Microsoft Windows uses Explorer as its default file manager. With Apple computers, Finder is considered the default file manager.

What is the latest storage device?

One of the most recent storage device technologies to be introduced is NVMe with SSDs and cloud storage also being a recently developed storage devices. Also, older technologies like hard disk drives and tape drives are always developing new techniques to allow for the devices to store more data.


Processor Components

A processor contains the following components,

  • Control Unit – fetches, decodes and executes instructions.
  • Arithmetic & Logic Unit – performs arithmetic and logical operations on data.
  • Registers – fast, on-chip memory inside the CPU, dedicated or general purpose.
  • Internal Clock – derived directly or indirectly from the system clock
  • Internal Buses – to connect the components
  • Logic Gates – to control the flow of information

The Processor or the Central Processing Unit

The CPU is also one of the most expensive components on the motherboard. It is a very delicate device and sensitive to ESD, thus it should be handled with care. The processor itself is a flat plate of silicon made up of millions of transistors etched on to the silicon plate to form a huge computer logic circuit.

A ceramic cover is placed over the micro-circuit to protect it and to conduct heat away to the heat sink. This protective ceramic covering will have print information of the processor type, speed, and other details.

How the Central Processing Unit Operates

The computer processor fetches, decodes, and executes program instructions. A computer program consists of a series of steps called instructions which tell the computer what to do. Each instruction can be a basic arithmetic calculation or a logic operation. Before the program can be executed it is loaded into the working space (memory).

It is the job of the microprocessor, which is controlling the computer to fetch a program instruction from the memory, decode the instruction and then carry out any action that might be needed which is the execution process. It is the responsibility of the processor inside the computer to carry out the fetch-decode-execute cycle over and over again operating from the instructions it obtains from the main memory.

This fetch – decode – execute cycle is often referred to as the fetch-execute cycle.

The CPU uses a timing signal to be able to fetch and execute instructions. The timing signal is provided by the system clock. The clock speed is measured in Hz (cycles per second). In early processors, speed was measured in Megahertz (MHz) is one million hertz (1 million cycles per second). Most of the computers we have today operate in the GHz (Gigahertz) range. The clock speed varies from one computer processor to another.


Key Components Found Inside the CPU

Arithmetic and Logic Unit (ALU)
This is the brain of the microprocessor. The ALU performs basic arithmetic calculations like adding, subtracting, multiplication and division of figures, it also performs logical operations like the comparison of figures

Control Unit (CU)

As the name suggests, this component controls all the functions that take place inside the processor itself. It instructs the ALU on which arithmetic and logical operation is to be performed. It acts under the direction of the system clock and sorts out all the internal data paths inside the processor to make sure that data gets from the right place and goes to the right place.

The Register

Register also sometimes known as the accumulator, is a temporary storage position where data coming from RAM heading to the processor for execution and data coming from the processor after processing is held. Thus a register is a local storage area within the processor that is used to hold data that is being worked on by the processor.

Internal Registers (Internal Data Bus)

This is the bus connecting the internal components of the processor to the motherboard. The size of the internal registers indicates how much information the processor can operate on at one time and how it moves data around internally within the chip. This is sometimes also referred to as the internal data bus. A register is a holding cell within the processor; for instance, the processor can add numbers in two different registers, storing the result in a third register. The register size determines the size of data on which the processor can operate.

External Data Path

This is the path (bus) used to fetch data from memory to the processor. In some cases, the internal and external data buses are the same bit-size but in others, the external data bus can be either narrower or wider. The external data path is normally not as wide as the internal data path.

Having a smaller external bus (data path) will slow the performance of the-CPU, but it makes it simpler to upgrade earlier system designs to a new processor. Having a larger external data bus will improve the performance as data can be brought into the CPU in large chunks.

The Address Lines

The address lines are used to specify the exact location in memory where data can be found. The standard PC is a binary device. Using the memory address bus, CPUs send out location information on their address lines (or control lines) and these address lines are routed to every other major component of the computer (memory, ROM, expansion bus etc).

The numbers of address lines within the memory address bus will determine the maximum number of addressable locations. For example, if a PC has 3 address lines the maximum number of addressable memory locations is 8.

What Is A Register?

Registers are storage locations within the circuitry of the CPU. They are very fast on-chip memory storing binary values using 32 or 64 bits. Information is held there while it is being interpreted or manipulated. Registers are dedicated or general purpose.

General Purpose Registers

Can be used by programmers to store data temporarily. Some computers may have up to 16 general purpose registers (R1…R16). Processor designers have assigned no specific role to these registers.

Stack Pointer (SP)

Points to a stack data structure holding return addresses, procedure or function parameters and local variables. Used when a procedure or function is called. Also used when an interrupt is serviced. (Interrupt = a signal from a source (hardware or software) requesting the attention of the processor)

Program Counter (PC)

Holds the address in main memory of the next instruction to be executed.

AKA Sequence Control Register (SCR) or Sequence Register.

Status Register (SR)

Contains bits that are set and cleared based on the results of an instruction. Allows the CPU to store information such as the occurrence of an overflow. This information can be used to decide whether or not to branch out of a given sequence of instructions.

The Accumulator

Holds the result of the current set of calculations. The instruction ADD #25 means add the value 25 to the contents of the accumulator and store the result in the accumulator.

Current Instruction Register (CIR)

Stores operator and operand for the current instruction.

Eg LDA 1000 (Load location 1000 into Accumulator)

LDA operator what you do
1000 operand what you do it to

Memory Address Register (MAR)

Holds the address of the memory location from or to which data is to be read or written. This could be the address of an instruction to be fetched or the address of data to be used in the instruction. When fetching instructions, copies the contents of the Program Counter.

Memory Buffer Register (MBR)

AKA Memory Data Register (MDR) Temporarily stores data read from or written to memory. CPU and Memory operate at different speeds (hence buffer)

Eg LDA 1000 placed here en route to the CIR for decoding.

Operand (1000) placed in MAR. Contents of 1000 copied to the MBR.

System Clock

Every computer has a system clock. The clock is a quartz controlled oscillator supplying timing signals at a fixed rate. Other timing signals are derived from this. These signals are used to regulate the execution of instructions and to synchronise the operation of the computer components.

Clock Speed

Processors are designed to execute instructions at a particular frequency. Expressed in Megahertz or Gigahertz. Some instructions require more ticks of the clock than others.

Word Length

The word is the smallest chunk of memory that a program can refer to independently. The length of the word limits the complexity of the instruction set and the efficiency of mathematical operations.

Bus Width

This term refers to the number of parallel wires allocated to a bus. The number of wires determines how large a word can be transferred over the bus. Each wire can transfer a binary digit. Word size increases with bus width.

Factors Affecting Performance

The performance of a computer system can be measured by running standard programs on the processor and assessing the number of machine operations completed for each unit of time.

Measured in GOPS – Giga-Ops Per Second (or MOPS)

Increase Clock Speed

The more transistors packed into the same space, the more heat generated by their operation. Quantum physics suggests theoretical limits on transistor size. Similarly, the higher the frequency of clock ticks, the more heat generated. Both factors place limits on clock speed.

Multicore Processors

Processors are arranged into several cores. Each core runs at a lower frequency. Multiple tasks are run at the same time on different cores or tasks are split across several cores. Multicore processors are particularly suited to multimedia work.

Increase Word Length

Typical processor word lengths are 32bit and 64bit. General purpose registers usually have a similar word length. The bigger the word length, the bigger the operands and the results. When an operand is larger than the word length, it must be split into multiple instructions, requiring more clock ticks. Word length also limits the number of storage locations that can be addressed in main memory. For this reason, there is a limit on how much memory can be addressed in a computer system with a 32bit word size.

Increase Bus Width

The system bus between the processor and main memory accounts for the worst time penalty in processing. The wider the bus, the larger the word that can be transferred along it. Where an address or instruction is wider than the bus, multiple clock ticks are required for processing.




ASSIGNMENT : CS5: Computer Hardware Assignment MARKS : 10  DURATION : 1 week, 3 days


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