Peripheral devices are devices connected to the computer but external in relation to the processing unit. If a peripheral device is disconnected, the computer will still be able to work; only functions performed by this peripheral device will not be available. For example, if you disconnect a keyboard, you would not be able to type in information but you will be able work with the graphical user interface by clicking the mouse. If you remove the hard disk, you will have to start up your computer using floppy disk and you will have to save your data on floppy disks only but the computer will still be working.
Peripheral devices can reside inside the computer case or outside. For example, a mouse, a keyboard, a monitor are always outside the case and they are connected to the computer via ports which are situated on the back of the case. Disk drives are positioned inside the case and they are connected to the motherboard via disk controller cards which are inserted in the expansion slots on the motherboard.
Peripheral devices are classified according to the purpose they serve:
Input devices are used for data input
Output devices are used for data output
Storage devices are used to store data for long periods of time
Every year new more sophisticated devices appear on the market and prices on existing devices drop down dramatically.
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