Introduction to

Computer

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

Input Devices

Scanner

Joy Stick

Touch PadLight Pen

Tablet

Touch Screen

Keyboard Keyboard was the first input device to be used with computers

and it is still the major and most widely used among all the input devices.

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.

Introduction to Keyboard

Function keys(F1-F12)

Alphabetic keys

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).

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

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 programs.

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 Ctrl key.

F10: Shows the Menu bar in Firefox and IE F11: Opens full screen mode in Windows Explorer and all

browsers F12: Opens Save As window on MS Office. Ctrl + Shift + F12 is

equivalent to Ctrl + P on MS Office

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 KEY(shortcut key)

How the computer accepts input from keyboard

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 controller ).

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 Controller

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 keyboard buffer

3. The keyboard controller sends an interrupt request to the system software

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 from keyboard

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, DVORAK, Chord

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

Limitations of QWERTY The original QWERTY keyboard suffers from the following

problems that Dvorak himself identified:1. Many common letter combinations require awkward finger

motions.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.

was, were)4. Most typing is done with the left hand, which for most

people is the weaker hand. It reduces the speed5. About 52% of typing is done on the top row, only 32% on the

home row and 16% on the bottom row

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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 Dvorak layout.

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.

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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.

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)

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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 actual letter.

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 using it.

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 conditions.

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

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 high4. Lack of familiarity5. Some people find to be very slow process of typing6. It increase fatigue as the work is done with a single hand

Mouse 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 four actions:

1. Clicking2. Double clicking3. Dragging4. Right clicking

Mouse 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 Douglas Englebart

Types of Mouse A mouse can be classified in several ways. According to the working mechanism a mouse can be three

types:1. Mechanical 2. Optomechanical3. Optical A mouse can be three type according to how a computer

mouse hooks up or connects to the computer:1. Serial mouse2. PS/2 mouse3. Cordless mouse

Basic Parts of a Mouse Almost all mice today do the translation using five

components: 1. A Ball2. Two rollers3. An infrared LED and an infrared sensor4. On-board processor chip5. A shaft

1. A ball inside the mouse touches the desktop and rolls when the mouse moves.

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

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:

                                

Typical optical encoding disk: This disk has 36 holes around its outer edge.

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 infrared LED (clear) on one side of the disk and an infrared sensor (red) on the other.

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 connector

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

How Mechanical Mouse Works?

A mechanical mouse incorporates an internal ball that comes in contact with the surface on which the mouse has been placed.

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.

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 of light.

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.

Optical Mouse

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 smoothly.

Optical mice have several benefits over wheeled mice: 1.Able to work on almost any surface2.No moving parts means less wear and a lower chance of failure. 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

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) 3. 0 4. 1 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, respectively.

References

1. Peter Norton book2. en.wikipedia.org

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Md. Shakhawat HossainStudent of Department of Computer Science & EngineeringUniversity of RajshahiE-mail: mshimul86@gmail.com