What is Hard Disk Drive

Hard Disk Drive is the mechanism that controls the positioning, reading, and writing of the hard disk, which furnishes the largest amount of data storage for the PC. Although the hard disk drive and the hard disk are not the same thing, they are packaged as a unit and so either term is sometimes used to refer to the whole unit. There are several interface standards for passing data between a hard disk and a computer. The most common are IDE and SCSI.

A single hard disk/drive usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders A hard disk/drive unit comes with a set rotation speed varying from 4500 to 7200 rpm. Disk access time is measured in milliseconds. Although the physical location can be identified with cylinder, track, and sector locations, these are actually mapped to a logical block address (LBA) that works with the larger address range on today's hard disks.