Basic Input/ Output Device System

Basic Input System

An input device is a peripheral used to provide data and control signals to an information processing system such as a computer or information appliance. Examples of input devices include keyboards, mouse, scanners, digital cameras and joysticks etc. Each of the device is explained below.


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 keyboard is connected to a computer system using a cable or a wireless connection.

A standard keyboard has 102 to 110 keys and with 256 to 260 characters and each key sends a different signal to the CPU. 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 and 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.


The Basic PC Keyboard Layout


A keyboard typically contains keys for individual letters, numbers and special characters, as well as keys for specific functions. There are four main keys on PC’s keyboard.

Function keys: These keys are positioned on the top row of the keyboard which are labeled as F1, F2, F3, and on up to F11 and F12. 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: To open help window.

F2: To used to rename a file or folder. Alt + Ctrl + F2 opens the Documents Library while on MS Office suite.

F3: To 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: To 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: To focuses on the address bar.

F7: To turns on browsing on Mozilla Firefox. F8: To enters the Windows Start Menu.

F9: To compiles and runs the code in combination with Ctrl key. F10: To shows the Menu bar in Firefox and IE.

F11: To opens full screen mode in Windows Explorer and all browsers. F12: To opens Save As window on MS Office.

Typewriter keys: These keys are the same types of keys that find on an old typewriter. All letters, numbers, and punctuation symbols include:

Cursor-control keys: These four arrow keys move the text cursor in the direction of their arrows. There are more six-pack cursor-control keys such as Insert, Delete, Home, End, Page Up and Page Down.

Numeric keypad: The numeric keypad contains calculator-like keys which are popular with accountants, bank tellers and airline ticket agents.

Typical Windows QWERTY keyboard
Typical Windows QWERTY keyboard

Types of Computer Keyboard

There are two major keyboard layouts being used worldwide:

(i) Standard keyboard (qwerty): It is named after the first six leftmost letters on the top alphabetical line of the keyboard. Also called a QWERTY keyboard because of the layout on its typing area. It has about 103 keys and about 257 characters.

(ii) Multimedia keyboard: It is designed for the user to access often-used programs such as Internet, music and email. It contains buttons that control various computer processes, such as turning on the computer's power, putting the CPU to sleep and waking it up again. It comes in various connection formats, including PS/2, USB and wireless.

Types of Keys on a Computer Keyboard

(i) Alphanumeric keys: All of the letters and numbers on the keyboard A-Z and 0-9. This arrangement is called the QWERTY because the first SIX keys on top of the row of letters are Q, W, E, R, T, Y. The numeric keypad looks like a calculator’s keypad, with its 10 digits and mathematical operators (+, - , *, /) . ? Numeric keys also features NUM LOCK key.

(ii) Punctuation keys: All of the keys associated with punctuation such as the comma, period, semicolon, brackets, parenthesis and so on. Also, all of the mathematical operators such as the plus sign, minus sign, and equal sign.

(iii) Special keys: He standard keyboard contains special key such as:

• Alt key – Short for Alternate, this key is like a second control key.

• Arrow Keys – Most keyboards have four arrow keys that enable to move the cursor up, down, right or left.

• Backspace key – Deletes the character just to the left of the cursor and moves the cursor to that position.

• Caps Lock Key – A toggle key that, when activated, causes all alphabetic characters to be uppercase.

• Ctrl key – Short for Control, this key is used in conjunction with other keys to produce control characters. The meaning of each control character depends on which program is running.

• Delete Key – Sometimes labeled Del, deletes the character at the current cursor position or the selected object but does not move the cursor. For graphics-based applications, the Delete key deleted the character to the right of the insertion point.

• Enter Key – Used to enter commands or to move the cursor to the beginning of the next line. 
Sometimes labeled Return instead of Enter.

• Esc Key – Short for Escape, this key is used to send special codes to devices and to exit (or escape) from programs and tasks.

• Function Keys – Special keys labeled F1 to F12. These keys have different meaning depending on which program is running.


Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object, it can roll along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse’s tail, and the fact that one must make it scurry along a surface. As user move the mouse, the pointer on the display screen moves in the same direction.

Types of Mouse

Based on their ports, there are three common types namely:

(i) PS/2 mouse

(ii) USB mouse

(iii) Serial mouse

Based on their designs, there are three common types namely:

(i) Mechanical mouse: It is a device integrated with an internal metal or rubber ball, which can spin in all directions (left, right, up and down). Thus, the display cursor moves as the mouse detects the direction. The ball in the mechanical mouse spins when it comes in contact with surface on which it is placed. A mouse pad should be used under the mouse to run on.

(ii) Optomechanical mouse: This type of computer mouse is the same as the mechanical mouse except that it uses optical sensors to the motion of the ball. A mouse pad should be used under the mouse to run on.

(iii) Optical mouse: This type of mouse uses a LED sensor for detecting the mouse's movement. This mouse doesn’t have mouse ball and electromechanical transducer. Movement is detected by sensing changes in reflected light, instead of interpreting the motion of a rolling sphere. This type mouse responds more quickly and precisely than the mechanical and optomechanical mouse. An optical mouse does not have moving parts. That is why there is no need of cleaning. Even user don't need a mouse pad.

(iv) Wireless mouse: The Mouse without wire or cord is called wireless mouse or cordless mouse. Most wireless mice use radio frequency (RF) technology to communicate information to computer.

Digital Camera

Images can be input into a computer using a digital camera. The digital camera takes a still photograph, stores it, and then sends it as digital input into the computer.

The images are then stored as digital files. These images can then be manipulated in many ways using the various imaging tools available.


Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image; dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in (For color and gray scaling, the same principle applies but each box is represented by up to 24 bits).


Trackball is another pointing device. Essentially, a it is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons near to the ball, which you use just like mouse buttons.


A lever that moves in all directions and controls the movement of a pointer of some other display symbols. A joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse.

Most joysticks include two buttons called triggers. Joysticks are used mostly for computer games, but they are also used occasionally for CAD/CAM systems and other applications.

Light Pen

Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen. It is similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing at the objects with the pen.

Digitizing Tablet

This is an input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called puck) is similar to a mouse, except that, it has a windows with cross hairs for pinpoint placement and have as many as 16 buttons.

A pen (also called a stylus), which looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronics that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer.


A small, touch-sensitive pad is used as a pointing device on some portable computers. It is consisting of specialized surface that can translate the motion and position of a user’s fingers to relative position on screen. It is also called trackpad.

Optical Mark Reader (OMR)

Optical marks are commonly used for scoring in tests. It is marked by the person taking the test, and can be read by the optical mark reader. The optical mark reader when online to the computer systems, can read upto 2,000 documents per hour. Seemingly this rate is slow but the fact that transcription has been eliminated, the overall time is less than those of conventional file media.

Handwriting Recognition Device: OCR

Often abbreviated OCR, optical character recognition refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate (for example, into ASCII codes). As OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file.

Magnetic Ink Character Recognition (MICR)

An MICR can identify and decode characters printed with a special ink that contains particles of magnetic material. The reading process is called Magnetic Ink Character Recognition.

Bar Code Reader

You are probably familiar with the bar code readers in supermarkets, bookshops, etc. Bar-code readers are photo electric scanners that read the bar codes, or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC).

Speech Recognition Device: Microphones

A speech recognition program can process the input and convert it into machine-recognized commands. It is also known as Speech Input Device.


A web camera (or webcam) is a real-time camera whose images can be accessed using the World Wide Web, instant messaging or a PC video calling application.

Basic Output System

Output is anything that comes out of a computer. Output can be meaningful information or gibberish, and it can appear in a variety of forms – as binary numbers, as characters, as pictures, and as printed pages. An output device is any machine capable of representing information from a computer. Output devices include display screens, loudspeakers, printers, plotters, etc.


A computer monitor, technically termed as visual display unit is an output device that presents the information from the CPU on the screen working as an interface between CPU and the user. A cable connects the monitor to a video adaptor or video card which is set up on the motherboard of the computer. The CPU (Central Processing Unit) sends instruction to the video adaptor telling what needs to be displayed on the screen. The video adaptor converts the instructions into a set of corresponding signals and sends to the monitor. Monitor contains a circuitry that generates the picture on the screen from the set of signals.

Types of Computer Monitor

Most people use computer monitors daily at work and at home. And while these come in a variety of shapes, designs and colors, they can also be broadly categorized into three types.

1. CRT Monitor: CRT stands for Cathode Ray Tube. These monitors employ CRT technology, which was used most commonly in the manufacturing of television screens. CRT stands for Cathode Ray Tube. A cathode ray tube is basically a vacuum tube containing an electron gun at one end and a fluorescent screen at another end. These guns generate red, green and blue (RGB) colors which are generated other color with a combination of these three colors. Nowadays, most of the CRT monitors are replaced by LCD and LED Monitors. The main disadvantages are heavy weight, occupy more place, high power consumption, high radiation and supports low resolution.

2. Flat-panel Monitor: Flat-panel monitor is a thin screen display found on all portable computers and is the new standard for desktop computers. Flat panel displays use liquid- crystal display (LCD) or light-emitting diode (LED) technology to make them much lighter and thinner compared to a traditional monitor. Actually there are no differences between LCD and LED monitors but better picture quality in LED monitors.

Types of Computer Monitor

Types of Computer Monitor


Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories. Printers are output devices that print documents and reports. Printers are of two major categories:





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