Keyboard And Mouse

Objectives :

  • Explain the working of the keyboard
  • List the types of keyboards
  • List the types of keyboard connectors
  • Explain connection of keyboard to computer
  • Troubleshoot the keyboard
  • Explain the working of the mouse
  • List the types of mouse connections
  • List the types of mice
  • Explain connection of mouse to computer
  • Troubleshoot the mouse

Keyboard :

Primary input device of the computer and used to enter commands and type text. It’s similar to typewriter.

Present day keyboards have 101 or more keys


Main types of keys on a Windows keyboard are :

  • Alphanumeric – Enables the user to enter text and numbers
  • Punctuation – Enables the user to punctuate sentences and add additional characters
  • Navigation – Used to move the cursor between different places on a screen
  • Special – Perform some special functions on the data
  • Windows – Open Windows-specific items like the Start menu
  • Function – Used to perform certain functions like provide help
  • Numeric – Enables the user to perform numerical operations on the data
  • Modification – Enables the user to use additional features like capitalizing letters (caps lock)

Types of Keyboards :

PC/AT keyboard was a part of the PC/AT computer introduced by IBM and it had 84 keys

101-Key Enhanced – major drawback – a small Enter key. This layout continues to be used even today

102-Key Enhanced – for non-English users

104-Key Windows – Microsoft introduced this key board. Three keys included are two identical keys to open start menu and one key to perform the right click

Ergonomic – designed keeping in mind the comfort of the user and also known as natural key board. It includes wrist rests and the angle between two halves can be adjusted. It is difficult to use if you are not experienced typist. It is expensive and consume more space

Programmable – an important key is Remap. User can swap the keys. It will be in effect even if the keyboard is connected to another computer. It can also create macros. It’s not very popular as most users consider the additional features unnecessary. If the keyboard is not used carefully it could change functions of important keys without user even realizing it

Multimedia – added functionality to open mail clients, multimedia player, internet browser and search programs, go back and forth in web browser, volume control and jump from one file to another in a multimedia player

Cordless -

Keyboard Connectors :

5-pin DIN5 connector


6-pin PS/2 connector


4-pin USB connector


Working of the Keyboard :

Has a microprocessor that studies the state of each key on the keyboard and sends the appropriate signal to the computer

Grid of circuits underneath keys on keyboard known as key matrix

Circuits below all keys are broken

Circuit is closed, and microprocessor detects closed circuit – when pressing a key

Microprocessor detects the closed circuit and notes the position of the circuit on the key matrix

Microprocessor has a character map of the keyboard in its ROM

Compares the location of the closed circuit to the same location in the character map

Processor analyses the key matrix and decides on the characters to be sent to the computer through a connector

When you press a combination of characters, processor compares the combination to character map and see if there is any designation for that particular combination

These characters are maintained in am memory buffer and then sent in a stream to the computer

Troubleshooting the Keyboard :

Keyboard is a largely a trouble-free device if handled properly

Do not spill liquids or food particles on the keyboard

Problem that may occur with keyboards are :

  • Computer may display keyboard error
  • Keyboard is not working properly

Mouse :

Douglas Engelbart invented mouse

The name is so because the appearance and movement are very similar to that of a mouse

Enables user to move cursor or pointer to specific point on screen

Can have two or three buttons or a scroll button

When you move the mouse, the cursor on the screen also moves in the same direction

Mouse is important for Graphical User Interface (GUI) applications

You can use the mouse to draw objects on the screen

Types of Mouse Devices :

Mechanical Mouse – consists of rubber or metal ball and mechanical sensors (VARIAC)


Optomechanical Mouse – use optical sensors instead of mechanical sensors and more accurate


Optical Mouse – uses laser technology and most accurate and precise type of mouse.


Cordless Mouse – uses an infrared or radio link and operates on batteries


Mouse Connectors :

Serial Connector


PS/2 Connector


USB Connector


Working of Mouse :

Mouse converts the movements to signals that the computer can use

Mouse has a ball inside its body that rolls around as mouse is moved

Two rollers are angled so that one senses the movement of the mouse ball in the X-direction and the other in the Y-direction and touch the ball

Roller connected to a shaft and shaft moves a disk that has many holes in its periphery

Infrared LED provides light, which shines on the disks

As the disk rotates, the beams of light are broken due to the gaps between the holes on the disk

Infrared sensor senses pattern of light

Mouse processor receives signals form the sensor and converts signals to binary data

Send to the computer through cord and connector

Connecting the mouse :

If you installed a serial mouse, check the CMOS settings to ensure that the serial or COM ports are enabled and assigned

If you installed a USB mouse, check the CMOS settings to ensure that the USB is enabled. Also ensure that USB legacy support is enabled

Troubleshooting the Mouse :

Mouse can give problems if not handled with care

Do not spill liquid or other substances around the mouse

Problems that may occur with mouse are :

  • Mechanical Mouse is not moving properly
  • Cordless Mouse is not moving properly
  • System does not recognize mouse
  • Mouse does not move in a particular direction
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