Floppy Disk
A floppy disk or a diskette is a round flat removable piece of plastic coated with a Ferric Oxide layer, and encased in a protective plastic cover, called the disk jacket. The Ferric Oxide layer is capable of holding a magnetic field. Data is stored on a floppy disk by means of a disk drive, which alters the magnetic orientation of the particles in the Ferric Oxide layer. Reading data from a diskette means that the data stored as a magnetic pattern on a diskette is converted to electronic signals and transmitted to the memory of the computer. Writing data on a diskette means electronic information is transformed into magnetic patterns and recorded magnetically on the diskette.
Evolution of Diskettes
Year Introduced
|
Physical Size
(in inches)
|
R/W Capability
|
Maximum Capacity
|
Number
of
sides used
|
1970
|
8
|
R
|
100 Kilobytes
|
Single
|
1973
|
8
|
R/W
|
250 Kilobytes
|
Double
|
1976
|
5.25
|
R/W
|
100 Kilobytes
|
Single
|
5.25
|
R/W
|
1.2 Megabytes
|
Double
| |
1980
|
3.5
|
R/W
|
1.44 Megabytes
|
Double
|
Zip disks and Jaz disks
These disks are very similar to floppy disks except that they can be used to store large amounts of data. Zip disk capacities from 100 to 750 MB and Jaz disks come in 1 and 2GB capacities. Both these disks are removable and portable and provide much better performance than floppy disks.
Magneto optical disk
Magneto optical disk drives use a combination of a laser, to heat the surface of the disk, and a magnetic head, to record data. While these disks are high performance, they are expensive. Magneto optical disk have capacities ranging from 128 MB to several Gigabytes.
Magnetic tapes are similar to audio tapes and store data in a serial manner (i.e. data is stored one after the other on the tape). These tapes can store large amounts of data but are primarily used for backup because the access speeds are slow.
CD/DVD
A Compact Disk (CD) is a plastic disk where disk is optically 'written' on its surface. The data written on the disk is read using a CD-ROM drive which uses lasers for this purpose. Usually once the data has been 'written' (or 'burnt') on to the CD, it is not possible to change it, hence Read Only Memory. Some CDs are re-writable. To 'write' to a CD, a drive called 'CD Writer' must be used. The faster the CD ROM drive can read a CD, the faster the computer will be able to get data from the CD. Digital Versatile Discs (DVD0 use a similar concept to CDs except that are able to use multiple surfaces on a single disc and so can be used to store larger amounts of data. A typical CD can store 650 to 700 MB of data while a DVD can store from 2GB to 8GB of data.
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