Chapter 9: Hard Disks and Floppy Disks^171
it encloses form what is called theHead Disk Assembly (HDA). The HDA is a sealed unit
that is never opened.
The following sections provide an overview of each of the hard disk’s components.
Disk Platters
Whether you call themplattersordisks, as they are more commonly called, the primary
unit of a hard disk drive is its disks. The disks are the storage media for the disk drive and
it is on them that the data is actually recorded. Disks are made from a number of different
materials, each with its own performance and storage characteristics. The primary
two materials used in disks are aluminum alloys and glass.
The traditional material for platters was an aluminum alloy, which provided strength
yet was lightweight. However, because aluminum disks tend to flex by expanding under
heat, many disk drives now use a glass-ceramic composite material for disk platters. The
platters of the disk drive, whether aluminum or glass are rigid (the source of the name
harddisk), unlike the flexible disk in a floppy disk.
Figure 9-1. The major components of a hard disk drive. Original photo courtesy of Western
Digital CorporationActuator shaftData connectorVoice coil
actuatorPower connectorAir filterJumpersHead armRead/write headsPlatters Spindle