Many types of HDDs are on the market, but nearly all share the same basic physical components.
Some differences might exist in the implementation of these components (and in the quality of the materials used to make them), but the operational characteristics of most drives are similar. The basic components of a typical HDD are as follows (see Figure 9.9):
■ Disk platters
■ Read/write heads
■ Head actuator mechanism
■ Spindle motor (inside platter hub)
■ Logic board (controller or Printed Circuit
■ Cables and connectors
■ Configuration items (such as jumpers or switches) Hard Disk Platters (Disks)
An HDD has one or more platters, or disks. Hard disks for PC systems have been available in several form factors over the years. Normally, the physical size of a drive is expressed as the size of the platters.
Table 9.9 lists the platter sizes that have been associated with PC HDDs. with PC systems. Currently, the 3 1/2-inch drives are the most popular for desktop and some portable systems, whereas the 2 1/2-inch and smaller drives are popular in portable and notebook systems.
Most HDDs have two or more platters, although some of the smaller drives used in portable systems and some entry-level drives for desktop computers have only one. The number of platters a drive can have is limited by the drive’s vertical physical size. The maximum number of platters I have seen in any 3 1/2-inch drive is 12; however, most drives have six or fewer.
Platters were originally made from an aluminum/magnesium alloy, which provides both strength and light weight. However, manufacturers’ desire for higher and higher densities and smaller drives has led to the use of platters made of glass (or, more technically, a glass-ceramic composite). One such material, produced by the Dow Corning Corporation, is called MemCor. MemCor is composed of glass with ceramic implants, enabling it to resist cracking better than pure glass. Glass