Hardware components, involved in the function of a computer. computer hardware consists of the components that can be physically handled. The function of these components is typically divided into three main categories:

1.INPUT DEVICES,
2.OUTPUT DEVICES,
3.STORAGE DEVICES.

I.COMPUTER INPUT DEVICES

An input device consists of external devices that is, devices outside of the computer's CPU that provide information and instructions to the computer.

1.LIGHT PEN:
A light pen is a stylus with a light sensitive tip that is used to draw directly on a computer's video screen or to select information on the screen by pressing a clip in the light pen or by pressing the light pen against the surface of the screen. the pen contains light sensors that identify which portion of the screen its passed over.

2.MOUSE:
A mouse is a pointing device designed to be gripped by one hand. It has a detection device (usually a ball) on the bottom that enables the user to control the motion of an on - screen pointer, or cursor, by moving the mouse on a flat surface. As the device moves across the surface ,the cursor moves across the screen .To select items or choose commands on the screen ,the user presses a button on the mouse .

3.JOY STICK:
A joystick is a pointing device composed of a lever that moves in multiple directions to navigate a cursor or other graphical object on a computer screen.

4.KEYBOARD:
A keyboard is a type writer - like device that allows the user to type in text and commands to the computer some keyboards have special function keys or integrated pointing devices, such as a trackball or touch - sensitive regions that let the users finger motions move an on screen cursor.

5.OPTICAL SCANNER:
An optical scanner uses light - sensing equipment to convert images as a picture or text in to electronic signals that can be manipulated by a computer.

6.MICRO PHONE:
A micro phone is a device for converting sound into signals that can then be stored, manipulated, and played back by the computer.

7.VOICE RECOGNITION:
A voice recognition module is a device that converts spoken words into formation that the computer can recognize and process.

8.MODEM:
A modem which stands for modulator-demodulator is a device that connects a computer to a phone line or a cable television network and allows information to be transmitted to or receive from another computer. Each computer that sends or receives information must be connected to a modem. the digital signal sent from one computer is converted by the modem into an analog signal, which is then transmitted by telephone lines to receiving modem which converts the signal back into a digital signal that the receiving computer can understand.

II. OUTPUT DEVICES

output hardware consists of external devices that transfer information from the computer's CPU to the computer user. A video display or screen converts information generated by the computer into visual information.

1.DISPLAY:
Displays commonly take one of two forms. a video screen with a cathode ray tube (CRT) or a video screen with a liquid crystal display (LCD).
a CRT based screen looks similar to a television set. information from the CPU is displayed using a beam of electrons that scans a phosphorescent surface that emits light and creates images.
An LCD based screen displays visual information on a flatter and smaller than a CRT based video monitor. LCDs are frequently used in laptop computers.

2.PRINTERS:
Printers take text and image from a computer and print them on a paper. Dot - matrix printers use tiny wires to impact upon an inked ribbon to form characters. Laser printers employ beams of light to draw images on a drum that then picks up fine black particles called toner. this is used to produce an image. Inkjet printers fire droplets on ink onto a page to form characters and pictures.

III. STORAGE DEVICES

Storage hardware provides permanent storage on information and programs for retrieval by the computer. The main types of storage devices are disk drives and memory.

1. HARD DISK DRIVE:
Hard disk drives store information in magnetic particles embedded in a disk. Usually a permanent part of the computer, hard disk drives can store large amounts of information and retrieve that information very quickly.

2.FLOPPY DISK DRIVE:
Floppy disk drives also store information in magnetic particles embedded in a removable disks that may be floppy or rigid. Floppy disk store less information than a hard disk drive and retrieve the information at a much slower rate.

3.MAGNETO OPTICAL DISK DRIVE:
Magneto optical disk drives store information on removable disks that are sensitive to both laser light and magnetic fields. they can typically store as much information as hard disks, but they have slightly slower than retrieval speeds.

4.COMPACT DISK DRIVE:
Compact disk drives store information on pits burned into the surface of a disk of reflective material. CD ROMs can store about as much information as a hard drive but have slower rate of retrieval. A digital video disk (DVD) looks and works like a CD ROM but can store more than 7 times as much information.

5.MEMORY:
Memory refers to the computer chips that store information for quick retrieval by the CPU. Random Access Memory is used to store the information and instructions that operate the computers programs.
typically programs are transferred from storage on a disk drive to RAM. RAM is also known as volatile memory because the information within the computer chips is lost when power to the computer turned off.
Read Only Memory (ROM) contains critical information and software that must be permanently available for computer operation, such as the OS that directs the computer actions from start up to shut down. ROM is called non volatile memory because the memory chips don't lose their information when power to the computer is turned off.