2. Input Devices
Input device: Devices that enable the user to enter data as
instruction into the computer for processing are called input
devices. It is used to supply data or information to a computer.
The most widely used input devices of the computer system:
keyboard and mouse.
Other examples: scanner, touch pad, light pen, tablet, digital
camera and joystick
Keyboard was the first input device to be used with computers
and it is still the major and most widely used among all the
It is the primary input device for entering text and numbers. It
is an arrangement of keys on a board in an organized way– this
is why it is called keyboard.
A standard keyboard includes about 100 keys and each key
sends a different signal to the CPU.
Keyboard includes the following types of keys: alphabetic keys,
numerical keys, function keys, cursor movement(arrow) keys,
modifier keys, scroll keys, punctuation mark keys and other
special purpose keys.
6. Different types of keys
Alphanumeric keys: alphanumeric keys composed of
alphabetic keys and number keys with a few keys(TAB, CAPS
LOCK, BACKSPACE, ENTER).
Modifier keys: The SHIFT, ALT(alternate) and CLTR(control)
keys are called modifier keys as they modify the input of other
keys. In other words, if a modifier key is held down while
pressing another key, then the operation or action of the second
key is changed in some way.
For example if the key “c” is pressed it will simply type a letter
“c”(small c). But if the key “c” is pressed with the modifier key
“CLTR” it will copy something. Again if key “c” is pressed with
the modifier key “SHIFT” then it will type a letter “C” (Capital C).
7. Different types of keys
Function keys: F1 to F12 these12 keys are called function keys.
They are used to perform special types of operation for the user.
Most IBM compatible keyboards have 12 function keys.
Though F1 through F12 have some default primary and
secondary features, they can be used well in combination with
keys like Ctrl and Alt.
F1: open help window
F2: used to rename a file or folder. Alt + Ctrl + F2 opens the
Documents Library while on MS Office suite
F3: used to find something. Shift + F3 toggles between capitalizing
each word, lower case and upper case for selected text on MS Word
F4: Alt + F4 closes the current program. If no program is running
then it launches the Shutdown dialog box
8. F5: used to refresh action. While using PowerPoint it is used to
start a slide show. Opens Find, Replace, Go to dialog on MS Office
F6: Focuses on the address bar on most browsers
F7: Could not figure out anything for Windows. Turns on Caret
browsing on Mozilla Firefox. This feature places a moveable cursor
in web pages, allowing you to select text with the keyboard.
F8: Enters the Windows Start Menu (commonly used to launch the
safe mode) if pressed during boot process
F9: Generally, compiles and runs the code in combination with
F10: Shows the Menu bar in Firefox and IE
F11: Opens full screen mode in Windows Explorer and all
F12: Opens Save As window on MS Office. Ctrl + Shift + F12 is
equivalent to Ctrl + P on MS Office
9. Different types of keys
Cursor movement keys(arrow keys): most standard
keyboards include a set of cursor movement keys, which enable
an user to move around the screen without using a mouse.
Special purpose keys: IBM compatible keyboards include eight
special purpose keys, each of which performs a unique function.
These keys are ESC, PRINT SCREEN, SCROLL LOCK, PAUSE,
INSERT, DELETE, WINDOWS KEY(start key), MENU
10. How the computer accepts input from
When a key is pressed, a tiny chip called the keyboard controller
notes that a key has been pressed. Then the keyboard controller
places a code into the keyboard buffer to indicate which key is
pressed (keyboard buffer is a part or memory of keyboard
Then the keyboard controller sends a signal to the computer’s
system software to tell that something has happened at the
keyboard. When the system software receives the signal, then it
reads the memory location in the keyboard buffer that contains
the code of the pressed key. Then the system software passes
the code to the CPU.
The keyboard buffer can store many keystrokes at one time. It is
necessary as the user may press multiple keys before the CPU
read a key from keyboard buffer.
Keyboard Buffer System Software
1. A key is pressed on the keyboard
2. The keyboard
controller sends the scan
code for the key to the
3. The keyboard
controller sends an
interrupt request to the
4. The system software
responds to the interrupt
by reading the scan code
from the keyboard buffer
5. The system software passes
the scan code to the CPU
How the computer accepts input
12. Types of keyboard
Keyboards can be classified in many ways. One efficient way is
to classify them according to their key arrangements. But they
can be classified in many more different categories depending
on types of computer connector, size, number of keys etc.
Here we will discuss three basic types of keyboard: QWERTY,
13. QWERTY keyboard The QWERTY keyboard was invented by Christopher Sholes
who was issued a patent for a typewriter on July 14, 1868. The
QWERTY keyboard is named after the five letter keys located at
the top left side of the keyboard and is now the official standard
of computer keyboards (ISO 9995). Today, the QWERTY
keyboard is the most commonly found and used computer
keyboard in the United States.
Top 6 Letter keys
14. Limitations of QWERTY
The original QWERTY keyboard suffers from the following
problems that Dvorak himself identified:
1. Many common letter combinations require awkward finger
2. Many common letter combinations require a finger to jump
over the home row.
3. Many common letter combinations are typed with one hand. (e.g.
4. Most typing is done with the left hand, which for most
people is the weaker hand. It reduces the speed
5. About 52% of typing is done on the top row, only 32% on the
home row and 16% on the bottom row
15. DVORAK keyboard
The Dvorak Keyboard is a keyboard layout developed in 1936
by Dr. August Dvorak and his brother-in-law.
Over the years several variations were designed. These
variations commonly known as the Dvorak keyboard or
The main objective of DVORAK keyboard is to make typing or
using of keyboard more rhythmic, user friendly, increase
speed, reduce effort and fatigue, thus reduce error.
16. DVORAK PRINCIPALS
Dvorak studied letter frequencies and the physiology of
people's hands and created a layout to alleviate the problems
he identified with the QWERTY layout. The principles:
1. Letters are typed by alternating between hands which
makes typing more rhythmic, increases speed, reduces
error, and reduces fatigue.
2. About 22% of typing is done on the top row, only 70% on
the home row and 8% on the bottom row.
3. The right hand should do more of the typing because most
people are right-handed. In other words it can be said that it is
little biased right handed people, that 56% of the keystrokes
are made with the right hand side. And the rest 42% with the
left hand. So it is equally biased and balanced.
17. DVORAK PRINCIPALS
4. The least common letters should be on the bottom row
which is the hardest row to reach.
5. The layout is also aims to minimize the number of
keystrokes made with the weak fingers
6. Experiments have shown that there is a speed
improvement of between 10 to 15%, coupled with the
reduction of user fatigue.
7. The Dvorak layout is intended for the English language.
(later few other languages also involved)
18. CHORD KEYBOARD
A chord keyboard is a computer input device that allows the
user to enter characters or commands by pressing several
keys together, like playing a "chord" on a piano.
This keyboard allows text or commands to be entered with
one hand, leaving the other hand free
Chord keyboards are significantly
different from normal alphanumeric
keyboards. Only a few keys, four or five, are
used and letters are produced by pressing
one or more of the keys at once. For
example, in the Microwriter, the pattern of
multiple key presses is chosen to reflect the
19. CHORD Keyboard Advantages
Such keyboards have a number of advantages:
1. They are extremely compact. It simply reduces the size of a
conventional keyboard makes the keys too small and close
together, with a correspondingly large increase in the difficulty of
2. This keyboard allows text or commands to be entered with
one hand, leaving the other hand free
3. Chord keyboards can be used in cramped and confined
4. Learning time for the keyboard is supposed to be fairly short
– of the order of a few hours
5. In particular, courtroom stenographers use a special form of two-
handed chord keyboard and associated shorthand to enter text at
full spoken speed
20. CHORD Keyboard Disadvantages
Such keyboards have a number of disadvantages:
1. It is considered to be very difficult to use.
2. Hard to learn
3. Social resistance is still high
4. Lack of familiarity
5. Some people find to be very slow process of typing
6. It increase fatigue as the work is done with a single hand
A mouse is an input device that functions by detecting two-
dimensional motion relative to its supporting surface.
Physically, a mouse consists of an object held under the user's
hands, with one or more buttons.
It is a hand-operated electronic device that controls the
coordinates of a cursor on the computer screen as the user
moves it around on a surface. It can be used only in graphical
user interface based computer system.
Mouse performs the pointing operation through the following
2. Double clicking
4. Right clicking
The computer mouse was invented by Douglas Englebart during
the 60's and was patented on November 17, 1970.
This mouse was first used with the Xerox Alto computer
system in 1973.
First Mouse invented by
23. Types of Mouse
A mouse can be classified in several ways.
According to the working mechanism a mouse can be three
A mouse can be three type according to how a computer
mouse hooks up or connects to the computer:
1. Serial mouse
2. PS/2 mouse
3. Cordless mouse
24. Basic Parts of a Mouse
Almost all mice today do the translation using five
1. A Ball
2. Two rollers
3. An infrared LED and an infrared sensor
4. On-board processor chip
5. A shaft
25. 1. A ball inside the mouse touches the desktop and
rolls when the mouse moves.
26. 2. Two rollers inside the mouse touch the ball. One of the rollers
is oriented so that it detects motion in the X direction, and the
other is oriented 90 degrees to the first roller so it detects
motion in the Y direction. When the ball rotates, one or both of
these rollers rotate as well. The following image shows the two
white rollers on this mouse:
The rollers that touch
the ball and detect X
and Y motion
27. 3. The rollers each connect to a shaft, and the shaft spins a disk
with holes in it. When a roller rolls, its shaft and disk spin. The
following image shows the disk:
encoding disk: This
disk has 36 holes
around its outer
28. 4. On either side of the disk there is an infrared LED and an
infrared sensor. The holes in the disk break the beam of light
coming from the LED so that the infrared sensor sees pulses of
light. The rate of the pulsing is directly related to the speed of the
mouse and the distance it travels.
There is an
(clear) on one side
of the disk and an
(red) on the other.
29. 5. An on-board processor chip reads the pulses from the infrared
sensors and turns them into binary data that the computer can
understand. The chip sends the binary data to the computer
through the mouse's cord.
The logic section of a
mouse is dominated
by an encoder chip, a
small processor that
reads the pulses
coming from the
infrared sensors and
turns them into bytes
sent to the computer.
You can also see the
two buttons that
detect clicks (on
either side of the wire
30. Mechanical Mouse
• This is a type of computer mouse that has a rubber or metal
ball on its underside and it can roll in every direction.
• There are sensors within the mouse, which are mechanical,
detect the direction in which the ball is moving and moves
the pointer on the screen in the same direction. A mouse
pad should be used under the mouse to run on
31. How Mechanical Mouse Works?
A mechanical mouse incorporates an internal ball that comes
in contact with the surface on which the mouse has been
The ball automatically rotates, when a user moves the mouse
on the surface or desktop.
Two wheels are used for detecting the rolling. Both the
wheels are placed at 90 degree angles from each other for
detecting mouse movements and its direction.
Here one wheel can detect up and down movements,
whereas, other is used for left and right movements.
Furthermore, the guide wheel (third wheel) that comes
loaded with spring pushes the ball against the two sensor
wheels for its functioning.
32. Optomechanical Mouse
This is the same as the mechanical mouse except that it
uses optical sensors to the motion of the ball. It demands
a mouse pad under the mouse to run on.
In optomechanical mouse, the disk moves mechanically,
and an optical system counts pulses of light. On this mouse,
the ball is 21 mm in diameter. The roller is 7 mm in
diameter. The encoding disk has 36 holes. So if the mouse
moves 25.4 mm (1 inch), the encoder chip detects 41 pulses
33. With advances in mouse technology, now-preferred device for
pointing and clicking is the optical mouse.
Developed by Agilent Technologies and introduced to the
world in late 1999, the optical mouse actually uses a tiny
camera to take 1,500 pictures every second.
34. How Optical Mouse Works?
Optical mouse has a small and red light-emitting diode (LED) that
bounces light off that surface onto a (complimentary metal-oxide
semiconductor) CMOS sensor.
The CMOS sensor sends each image to a digital signal processor
(DSP) for analysis.
The DSP operates at 18 MIPS (million instructions per second), is
able to detect patterns in the images and see how those patterns
have moved or changed since the previous image.
Based on the change in patterns over a sequence of images, the
DSP determines how far the mouse has moved and sends the
corresponding coordinates to the computer.
The computer moves the cursor on the screen based on the
coordinates received from the mouse. This happens hundreds of
times each second, making the cursor appear to move very
35. Optical mice have several benefits over wheeled mice:
1.Able to work on almost any surface
2.No moving parts means less wear and a lower chance of
3.There's no way for dirt to get inside the mouse and interfere
with the tracking sensors.
4.Increased tracking resolution means smoother response.
5.They don't require a special surface, such as a mouse pad.
Advantages of Optical Mouse
36. What Data is Sent?
When the mouse moves or the user clicks a button, it sends 4
bytes (32bits) of data to the computer. The first 8 bits contain:
1. Left button state (0 = off, 1 = on)
2. Right button state (0 = off, 1 = on)
5. X direction (positive or negative)
6. Y direction
7. X overflow (the mouse moved more than 255 pulses in
1/40th of a second)
8. Y overflow
The next 2 bytes contain the X and Y movement values,