I/O Devices (Input and Output devices)
Some devices work as both input as well Output devices. Examples are Floppy Disk
Drive, Hard Disk Drive, Computer Disk Drive (CD), Cassette Tape Drive, Modem, etc. Floppies, Cassette Tapes or CD’s require respective drive (for mechanical movement of the media) to be interfaced to the CPU for reading or writing data in to them.
In a FDD, the drive motor rotates disk at a speed of 300 – 360 rpm and the read/write head moves in contact with the recording surface of the disk. These heads work much like those in an audio cassette recorder. Diskette drive contain several sensor viz. write protect sensor, diskette sensor, media type sensor, etc. All PCs have a FDD controller which interfaces it with CPU.
The principle of working of Hard disk is same as that of a floppy diskette except for the fact that it is a stack of diskette. Each disk (platter) has recording surface on either side. It has more than two read/write heads. Hard disks can store a large amount of data/information. The maximum capacity in recent days is of the order of 4 GB. (About 3000 times that of a normal floppy) They are much more reliable than floppy disks.
The mechanism and principle of working of Cartridge Tape Drive (CTD) is similar to the one in an audio cassette recorder. The data/information can be recorded in the form of digitized signal on the magnetic media and read from the magnetic cassettes driven by these CTD. The storage capacity varies from 200 MG to 2 GB.
A compact disk (CD) is optical media in the form of a disk which is used to store data/information. A Compact Disk Drive (CDD) is needed to drive the CD. The storage capacity is approx 1000 times that of a floppy diskette.
Information can be written on storage media using these devices. Similarly, it can be read also. Thus, these devices are I/O devices.
A modem lets computers exchange information through telephone lines. One can use a modem to connect ones computer to another. One can use the facility to access internet and send and receive email message & faxes.