PC Hardware A Beginner’s Guide

(^172) PC Hardware: A Beginner’s Guide
Theglassplattersaremorerigidandassuchcanbelessthanhalfasthickasthealumi-
num disks. A glass disk does not expand or contract with changes in temperature, which
resultsinamorestableharddiskdrive.Mostofthetopharddiskmanufacturersuseglass
composite materials in their disk drives, including Seagate, Toshiba, and Maxtor. As the
disk drives continue to get smaller, storing more data, and operating at higher speeds,
glass materials are likely to be used in all disk drives.
Most PC hard drives generally have two platters. There are those with more (as many
as 10) and many have less (1 platter), especially smaller form factor drives. The number of
platters included in a disk drive is a function of design and capacity, which is controlled
somewhat by the overall size of the disk drive. Like the case, motherboard, and power
supply, a hard disk drive has aform factor. The form factor of a disk is essentially the size
of its platters, although it has also come to mean the size of the drive bay into which the
drive can be installed.
The more common form factors and their actual platter sizes are listed in Table 9-1.
There are disk drives in mainframes and other systems that have 8-inch, 14-inch, or
even larger platters. Of the form factors listed in Table 9-1, the 3.5-inch drive is currently
the most popular, having replaced the 5.25-inch drive, in desktop and tower-type PCs.
The 2.5-inch drive and 1.8-inch drives are popular in notebook computers.
Each platter is mounted on the disk spindle so that each side of the disk can be accessed
with a read/write head. The surface of each disk platter is polished and then covered with
alayerofmagneticmaterial,whichisusedtostoredata.Thediskspindle,read/writehead,
and how data is stored on the disk are all covered later in the chapter in more detail.
NOTE: In different publications and on some Web sites, you will seediskspelled asdisc. The two
spellings have become interchangeable, but there are those who still insist that the round platters
inside the disk drive are individually calleddiscs. Others, largely the CD-ROM and DVD folks, insist
that the termdiscis reserved to refer to optical disks. Either is fine—a disk is a disc is a disk—but you
will find thediskspelling used most often.
Form Factor Platter Size
5.25 inches 5.12 inches (130 millimeters [mm])
2.5 inches 2.5 inches (63.5 mm)
3.5 inches 3.74 inches (95 mm)
1.8 inches 1.8 inches (45.7 mm)
Table 9-1. Disk Form Factors