what is floppy disk

The floppy disk is a round plastic disk with iron oxide coating on it. Data is stored in iron oxide coating. The round disk is stored in a semi-rigid square-sized plastic casing. The casing works as the disk washer. Its inside is lined with a fleecy material. Dust is carried inside the casing and on the disk. When the disk rotates, the fleecy material inside the casing picks up the dust. Thus it works as disk washer.

There is one hole on the plastic casing so that data can be accessed (read or write) from the disk without removing the case. The casing also has another hole for write protection. If the hole is covered, then write is enabled (i.e., data in disk can be modified), If the hole open then no data can be written.

If the disk has iron oxide coating on both sides, then it can store data on both sides. This type of disks are called ‘Double Sided’ (DS) disks. Similarly if data is stored in double density then normal, then it is called ‘Double Density’ (DD) disk. In a ‘High Density’ (HD) disk the density of data is double than DD disks. For microcomputers normally two size of floppy disks are available: 3½ inch and 5¼ inch. Among all of these variations, the most popular diskette today is the 3½inch double-sided high-density disk with data storing capability of 1.44 MB.

Structure of the round disk :

A floppy disk consists of many concentric circles called tracks.
A track is divided in many semicircles called sectors.
A sector has many bytes.
A byte has eight bits.
Data is stored in Bits.

Floppy Disk Drive

The floppy drive contains the mechanism to rotate the disk inside the case and read/write data on it. The disk is inserted in the drive and then the drive performs these functions.

Data is read or written on the disk by disk head. For the double-sided disks today, the drive contains two heads one for each side.

Two stepper motors control the drive mechanism one rotates the motor and another moves the head from track to track. For example, to read data from sector-3 of track-2 of side-1 the following jobs are performed:

The head is moved on track-2 by one stepper motor.
The disk is rotated by another stepper motor, so that the sector-3 comes under the head.
Head of side-1 reads data from the disk.

The drive has a light. The light glows when one of the following things occur:

The drive reads data form the disk.
The drive writes data on the disk.
The cabling connection of the disk is not proper. The floppy disk drive has two connection points for cable:
One connection point has four pins. The power supply cable is connected here.
Another connection point has 34 pins. The flat cable that connects the ‘floppy disk drive’ with the ‘floppy disk controller’ is connected here.

Disk Controller

Disk controller contains the circuitry to control the floppy disk drive.

In XT type computers the floppy disk controller is built in a separate card called ‘floppy disk controller card’ which is inserted in the expansion slot of the motherboard.
In AT type computers, the floppy and the hard disk controllers are built in a single card called ‘disk controller card’. It is also inserted in the expansion slot of the motherboard.
In the PS/2 type computers and nowadays in the clones the disk controller circuitry is built in the motherboard.

Cable

The cable connects the floppy disk drive(s) with the controller. It has normally 3 edge connectors to connect the following devices:

The floppy drive ‘A:’
The floppy drive ‘B:’
The floppy-drive controller (i.e., today the motherboard).

It is a 34-wire flat cable. One of the wires is marked with dark (red or black) color. It is the wire number-1. The cable has a twist in one end. This end is connected with the floppy drive, which we want to use as drive ‘A:’

what is floppy disk