FLOPPY DISKETTES, HARD DISK

The floppy diskette is the most common and popular type of auxiliary storage. It provides computer system especially microcomputer system with the ability to read or retrieve information randomly. Diskettes are as real as paper files. Anything you can do with a paper file can be done with a disk file. This includes copying it. changing it, adding to it and changing its name. Floppy disks are flexible, made of oxide coated mylar and stored in a paper or plastic envelopes. The entire envelope is inserted in the disk unit, thus effectively protecting the contents of the disk surfaces. The disk surfaces are rotated inside the prtective covering. The disk head contacts the track positions through a solt in the covering. Recording is magnetic in conectric circles called tracks. These circles or track are divided into sectors. Each individual sector holds 512 bytes of data. Floppy or diskettes are available in three different sizes, the large size 8" diameter can hold information of the order of 360 kilohytes in the magnetic medium. The computer access the magnetic medium through the read/write opening. The index hole is used by the computer to properly align the diskette. Minifloppy diskette or 5.25" diameter floppy can hold information upto 1.2 megabytes while mircrofloppy diskette are of 3.5" diameter, and has capacity upto 1.44 megabytes. These drives and the diskettes used in them are referred to as "single sided/single density" or SS/SD, "single sided/double density" or SS/DD and also double sided/double density or DS/DD types. Generally microfloppy and minifloppy and assigned drive A and drive B respectively while the fixed hard disk drive is made the drive C. Various diskette deive configurations are used in addition to compact disk drive. They are housed in the system unit.

HARD DISK

Many computers contain a special type of disk called a fixed disk or hard disk. It is a high speed, large capacity disk and is referred as a mass storage magnetic medium that provides computer systems with the ability to read or retrieve informations sequentially or reandomly. The phsical characteristics of all magnetic recording material. Hard disks are faster and capable of storing much more information ranging in gigabytes. A typical hard disk unit consists or 6 circular disks fixed to a central shaft. Both surfaces of each plate are used to contain data except for the tep and bottom plaets. A set of disk plates can have 10 surfaces. For each recording surface there is a read/wirte head assembly. Each head can be positioned at any desired track/band on each surface. All the heads move together, therefore, the same recording band is selected on each recording surface at the same time. Thus for any single head movement the computer can access 10 bands of information.
LASER HOLOGRAPHIC STORAGE