Floppy Disk System

Floppy disks come in two sizes: 5¼ inch and 3½ inch. The 5¼ inch diskette is circular in shape with a hole in the center, called the clamping hole. It is covered with a square protective jacket. The jacket has an oval slot, called the head slot, which exposes a portion of the diskette surface. There is also a small hole near the center, called the index hole, which is the starting point of the diskette.

5¼ inch Floppy Disk

5¼ inch Floppy Disk

The diskette is inserted into the floppy disk drive, which is a sealed enclosure. It is clamped to the drive through the hub. The drive contains a spindle mechanism for rotating the diskette. It also contains another delicate piece of hardware called the read-write head that accesses the disk surface through the head slot and retrieves or stores data. The drive uses the index hole to sense the beginning of a track. The drive controller card supplies the drive with the necessary signals for its operations. For example, the controller tells the drive when to move the read-write head, when to start rotating the disk, and so on.

A 3½ inch diskette, also called as the microdisk, is also circular in shape and is covered with a square protective jacket. The media cover is pushed to expose the diskette surface. The operations are similar to those of 5¼ inch diskettes. A 3½ inch diskette is shown in Figure.

3½ Inch Diskette

A 3½ Inch Diskette

A diskette is divided into a series of concentric circles called tracks. The tracks are identified by numbers, with the outermost track as track zero. The tracks do not spread across the whole width of the recording surface, but take up a small area. The track is divided into sectors. Each sector is identified by a number that is assigned to it, starting with zero. Each type of floppy has a sector of a fixed size. A disk has two sides. Data can be recorded on either one or both sides of the disk.

The storage capacity of a disk is determined by factors like the number of tracks, sectors and the number of sides on which data is recorded. Depending upon the capacity of storage, the 5¼ inch diskettes are divided into double-density (360 KB) and high-density (1.2 MB).

The microdisk may be double-density (720 KB) or high-density (1.44 MB). Accordingly, disk drives can be double-density or high-density drives. A high-density drive can read and write on to a double-density diskette but the reverse is not possible.