Q. Components of magnetic disk?

Disk itself is mounted in a disk drive that comprises arm which is a shaft that rotates disk and the electronics required for input and output binary data. A non-removable disk is permanently mounted in disk drive. Hard disk in a personal computer is a non-removable disk. A removable disk can be replaced or removed with any other disk. Benefit of latter type is that unlimited amounts of data are available with a limited number of disk systems. In addition ZIP cartridge disks are illustrations of removable disks. Figure below illustrates other components of disks.

Figure: The Disk Components

Head mechanism provides a classification of disks in three types. Usually read-write head has been positioned at a fixed distance above platter allowing an air gap. At the other extreme is one head mechanism which in fact comes in physical contact with medium at the time of a read or write operation. This mechanism is used with floppy disk that is a small, flexible platter and the least costly type of disk.

To understand third type of disk we have to comment on relationship between distance of head from surface and data density. Head generates or senses an electromagnetic field of sufficient magnitude to read and write correctly.  The narrower head is the closer it should be to platter surface to function. A narrower head signifies narrower tracks and so greater data density that is desirable. But closer the head is to disk, greater are the risks of errors from imperfections or impurities.

To push technology advance Winchester disk was developed.  Winchester heads are employed in sealed drive assemblies which are nearly free of contaminants. They are designed to operate closer to disk's surface than conventional rigid disk heads so allowing greater data density. Head is in fact an aerodynamic foil which rest slightly on platter's surface when disk is motionless. Air pressure produced by a spinning disk is sufficient to make foil rise above surface. Resulting non-contact system can be engineered to use narrower heads which operate closer to platter's surface than conventional rigid disk heads.