Peripheral

Overview 

A peripheral is generally defined as any auxiliary device such as a computer mouse or keyboard, that connects to and works with the computer in some way. Other examples of peripherals areexpansion cards, graphics cards, image scanners, tape drives, microphones, loudspeakers, webcams, and digital cameras. RAM - random access memory - straddles the line between peripheral and primary component; it is technically a storage peripheral^{[citation needed]}, but is required for every major function of a modern computer and removing the RAM will effectively disable any modern machine. Many new devices such as smartphones and tablet computers have interfaces which allow them to be used as a peripheral by a full computer, though they are not host-dependent as other peripheral devices are. According to the most technical definition, the only pieces of a computer not considered to be peripherals are the central processing unit, power supply, motherboard, and computer case.

Usually, the word peripheral is used to refer to a device external to the computer case, like a scanner, but the devices located inside the computer case are also technically peripherals. Devices that exist outside the computer case are called external peripherals, or auxiliary components. Examples: "Many of the external peripherals I own, such as my scanner and printer, connect to the peripheral ports on the back of my computer."^[1] Devices that are inside the case such as internal hard drives or CD-ROM drives are also peripherals in technical terms and are called internal peripherals, but may not be recognized as peripherals by laypeople.

In a system on a chip, peripherals are incorporated into the same integrated circuit as the central processing unit. They are still referred to as "peripherals" despite being permanently attached to (and in some sense part of) their host processor.

Common peripherals

• Input
  • Keyboard
  • Computer mouse
  • Graphic tablet
  • Barcode Reader
  • Image scanner
  • Mic
  • Webcam
  • Other Input device
• Output
  • Display device
    • Computer display
    • LCD projector
  • Graphical output device
  • Printer
  • Other Output devices
• Storage
  • External hard drive
  • Flash drive
  • Disk drive, commonly within a hard drive enclosure
  • Smartphone or Tablet computer storage interface
  • CD-ROM drive
  • DVD-ROM drive
  • Other Storage Devices
• Input/Output
  • Modem
  • Network interface controller (NIC)
  • Touchscreen

Peripheral devices connect to the system unit through the ports on the computer

by : http://en.wikipedia.org/wiki/Peripheral