PC Hardware in a Nutshell, Second Edition

Chapter 14. Hard Disk Drives

Replacing the original hard disk or adding a hard disk is one of the most common upgrades. It’s easy to do, and a very cost-effective way to extend the life of a PC. This chapter explains what you need to know to choose, install, and configure hard disks and interfaces.

How Hard Disks Work

All hard disks are constructed similarly. A central spindle supports one or more platters , which are thin, flat, circular objects made of metal or glass, substances chosen because they are rigid and do not expand and contract much as the temperature changes. Each platter has two surfaces , and each surface is coated with a magnetic medium. Most drives have multiple platters mounted concentrically on the spindle, like layers of a cake. The central spindle rotates at several thousand revolutions per minute, rotating the platters in tandem with it.

A small gap separates each platter from its neighbors, which allows a read-write head mounted on an actuator arm to fit between the platters. Each surface has its own read-write head, and those heads “float” on the cushion of air caused by the Bernoulli Effect that results from the rapid rotation of the platter. When a disk is rotating, the heads fly above the surfaces at a distance of only millionths of an inch. The head actuator assembly resembles a comb with its teeth inserted between the platters, and moves all of the heads in tandem radially toward or away from the center of rotation.

Tip

Platters are cheaper than ...