What is the classification of magnetic disks

There are basically 5 types of drives:

  • Fixed head discs.
  • Disc packs.
  • Cartridge discs.
  • Winchester disks (hard drive).
  • Floppy.

We will briefly describe each of them below.

Fixed head discs.

They are discs that have an individual read/write head for each track, thereby achieving a relatively low access time, since this time is set solely by the speed of rotation of the disc. There are units with a single tray or with several trays.

Disc packs.

They are units made up of several plates that rotate together around a common axis. The read/write heads are mobile, with one per surface. These move simultaneously at high speed radially looking for the track where the sector to be written or read is located. All the heads move in unison, and each head reads/writes in the sector corresponding to its surface, transferring the information in parallel.

At a given instant, therefore, the same tracks are read/recorded from the different surfaces. Each group of these tracks is called a track cylinder, with as many cylinders as there are tracks.

Usually the outer surfaces are not used for recording, so a unit with 6 decks can only use 10 surfaces. There are disc pack units in which the discs are interchangeable.


It consists of a single platter with two recording surfaces. Usually these units are dual, that is, they contain two subsystems, one of them with a fixed platter (where the computer’s Operating System is recorded, for example) and the other with an interchangeable platter.

To remove the interchangeable disk, it is necessary to wait for the heads to retract and the disk to stop.

Winchester disks (hard disk).

A recent development is the Winchester disk. It is a disk of small size but of great precision and with a great storage capacity. It is permanently mounted on your drive.
The trays of these units are hermetically sealed and fixed. The fact that they are hermetically sealed is to reduce the effects of environmental dirt. It is not necessary to withdraw the heads at rest, as there is a specific “landing” runway. The heads are closer to the surface than in previous units, achieving high recording densities. Therefore, in small surfaces a lot of information can be stored.


Floppy disks are small discs whose plates are flexible, since they are made of a plastic material and are interchangeable.

Until recently, the most widely used floppy disks were 133 mm, also called mini-floppy disks, and currently the most widely used are 90 mm, also called micro-floppy disks.
The surface is protected by a cover covered internally with a material that facilitates the rotational sliding of the plate. In the sleeve there is a radial opening that covers all the tracks; through this window the floppy drive heads access information.
Also in the envelope and on the platter there is another hole that serves so that the optical drive has an alignment reference to locate tracks and sectors.

The center is open in order for the diskette to fit on the axis of rotation of the read/write drive. In the upper part of the right side there is a square notch, this indicates that the diskette is prepared to be able to record information on it, since it is not protected against writing.

The heads act in contact with the surface of the diskette.

The recording, depending on the type of unit, can be made on a single surface, that is, on only one of the sides, or on both sides.

Recording can also be done in normal density (or single density) or double density.

Floppy disks are excellent for acting as auxiliary mass memory for personal microcomputers. This is due to its relatively low price, being a direct access device and its high speed.

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