Computer Questions: How Floppy Disk Drives Work

The floppy disk drive was one of the first storage devices available to PC users and they are still use.

Floppy disk drives were the first computer storage devices to provide low cost secondary storage for personal computers. Floppy disks are so called because the original ones had a plastic covering over a flexible plastic disk. They were flexible rather than rigid, floppy rather than stiff. Floppy disks use the same technology for storing data that tape recorders use for recording sound. A thin plastic disc is coated with iron oxide. When it is subjected to a magnetic field, the particles in the oxide coating align themselves with the field. Computer data is in binary format which means a series of zeroes and ones. If we define alignment in a certain direction as a zero and in the opposite direction as a one, then we store data by varying the magnetic field according to the data values.

The first commercial floppies were about eight inches square. They consisted of an outer flexible plastic covering over a thin plastic (usually Mylar, a flexible but very strong plastic) disk. The disk was coated with iron oxide and the inside of the outer jacket had a coating that would capture small particles and provide a smooth, non-abrasive surface for the inner disc to spin against. The center of the inner disk had a hole through it and the outer jacket had a larger hole which left a ring of the inner disk exposed. There was a slot in the outer jacket that ran from the edge toward the center exposing the surface of the inner disc. The disk drive itself consists of a motor, the read/write head and the electronics to control both. When the floppy was inserted into the drive, the spindle of the motor went through the small hole in the inner disc and clamped against the exposed area of the inner disc. As the motor turned, the inner disc would spin inside its jacket. The read/write head pressed against the disc area exposed through the slot in the outer jacket. The read/write head moves back and forth along the slotted area and information is read from or written to the disc. The data is stored on the disk in circular rings.

The original 8 inch floppies could store about 64 Kb of data. These were referred to as single side, single density drives. The next technological step was to increase the density of the data and allow storage on both sides of the disk. Not surprisingly, these were known as double side, double (or high) density drives. As improvements continued to be made, the disk size was reduced to 5 ¼ inches and the amount of data that could be stored increased as well. The final entry in the floppy saga was not long in coming



The only floppy disk drive in anything like routine use today is the 3 ½ inch floppy. This is a floppy in name only. Its outer shell is hard plastic and its inner disk is metal covered with metal oxide. The outer shell is still coated on the inside to allow the inner disc to rotate without damage. It has a metal center hub and a spring loaded cover to protect the recording surface from contamination and damage. The drive itself is of course much smaller than either the 5 ¼ or 8 inch drives. When a disk is inserted, the drive mechanism pushes aside the cover and allows the read/write heads to contact the oxide surface. The motor grips the metal hub and spins the inner disk against the heads. Data is still read and written in the same basic manner except of course the 3 ½ inch disk holds 1.44 MB as opposed to the 8 inch disk's 64 Kb. Today floppy disks have been largely replaced as a storage medium by CD and flash memory for new systems but many existing systems still rely on them.

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