Hardware Reference
In-Depth Information
Figure 9.10. Typical HDD components.
The platters, spindle motor, heads, and head actuator mechanisms usually are contained in a sealed
chamber called the
head disk assembly
(HDA). The HDA is usually treated as a single component; it
is rarely opened. Other parts external to the drive's HDA, such as the logic boards, bezel, and other
configuration or mounting hardware, can be disassembled from the drive.
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.
Table 9.9. Hard Disk Form Factors Versus Actual Platter Sizes
Larger HDDs that have 8-inch, 14-inch, or even larger platters are available, but these drives are not
used 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
