Types of hard disks




Types of hard disks

Depending on packaging, hard disks are normally of three types -

Zip/ Bernoulli disk. It consists of a single hard disk platter encased in a plastic cartridge. Depending on the disk drive and size of disk, storage capacity varies from 8 GB to 500 GB or more. Its disk drive, called zip drive, may be of portable or fixed type. The fixed type is part of a computer system, connected to it permanently. A user can bring and connected the portable type to a computer system for the duration of use, and can then disconnect and take it away. We can load/unload a zip disk easily into a zip drive, just as we insert/remove a video cassette in a video cassette player.

Disk pack. It consists of multiple (two or more) hard disk platters mounted on a single central shaft. All disks revolve together at same speed. Its disk drive has a separate read/write head for each usable disk surface (recall that when a disk drive device uses multiple disks, the upper surface of the topmost disk and the lower surface of the bottommost disk are sometimes not used). The disk drive is of interchangeable type and allows users to load/unload different disk packs whenever required. When not in use, a user store a disk pack off-line in a plastic case. This gives virtually unlimited storage capacity to disk packs. Depending on the disk drive, size of disk, and number of disks in a pack, storage capacity of a single disk pack varies from few hundred GB to several thousand GB.

Winchester disk. A Winchester disk consists of multiple (two or more) hard disk platters mounted on a single drive central shaft. However, unlike a disk pack drive, a Winchester disk drive is of fixed type. That is, its hard disk platters and disk drive are sealed together in a contamination-free container and cannot be separate from each other. Hence, winchester disks have limited capacity. However, for the same number of disk platters of the same size, Winchester disks have large storage capacity than disk packs due to following reasons:

(a) As the disk platters and disk drive are sealed together permanently, all surfaces of all disk platters (including the upper of the topmost platter and the lower surface of the bottommost platter) are used data recording in a Winchester disk. That is, for a Winchester disk with four platters, there are eight Usable surfaces as opposed to six surfaces in case of a disk pack with four platters.

(b) Contamination-free environment allows Winchester disks to employ greater precision of data recording and accessing, resulting in greater data storage density than interchangeable disk packs. Winchester disks were so named the 30-30 Winchester rifle because the early Winchester disk systems had two 30-MB disks. Storage capacity of today's Winchester disks ranges from a few gigabytes (10/9 bytes ) to a few terabytes (10/12 bytes)