Q. Explain about hard drives?

Disks are generally mounted on a disk drive which comprises of an arm and a shaft along with electronic circuitry for read-write of data. Disk rotates along with shaft. A non-removable disk is permanently mounted on disk drive. One of most significant illustration of a non-removable disk is hard disk of PC. Disk is a platter coated with magnetic particles. Early drives were large. Later on smaller hard (rigid) disk drivers were created with fixed and removable pack. Every pack held about 30MB of data and became called as the Winchester drive. Storage capacity of today's Winchester disks is typically of order of a few tens of Megabytes to a few Gigabytes. Most Winchester drives have subsequent common aspects:

• Disk and read/write heads are enclosed in a sealed airtight unit.
• Disk(s) spin at a high speed, one such speed may be 7200 revolutions per minute
• Read/write head don't actually touch the disk surface
• Disk surface comprises a magnetic coating
• Data on disk surface (platter) are arranged in the series of concentric rings. Every ring is known as a track is subdivided into some sectors every sector holding a specific number of data elements known as bytes or characters.
• Smallest unit that can be written to or read from the disk is a sector. The storage capacity of disk can be determined as the number of sectors, number of tracks, byte per sector and number of read/write heads.

(a)  An Open Disk Casing

(b) Tracks and Cylinders

Figure: The Hard Disk