UPGRADING REPAIRING PCs

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Chapter 4—SCSI and IDE Hard Drives and Optical Drives
each sector for identifying the sector location on the hard disk.
These sectors form concentric circles numbering from the outside
of each platter to the hub area of the platter.
Cylinders
The third factor used to calculate the size of the hard disk is the
number of cylinders on the hard disk. The identically positioned
tracks on each side of every platter together make up a cylinder.
The BIOS calculates the size of the hard disk in MB—or more often
today, GB—from the number of cylinders, the number of heads,
and the number of sectors per track. Most BIOSs make this calculation
in binary MB or GB (the same way as the hard disk preparation
program FDISK does), but a few make the calculation in
decimal MB or GB (see Chapter 1, “General Technical Reference,”
for the differences in these numbering methods). BIOSs that use
decimal MB or GB calculations report the size of the drive the same
way that drive manufacturers do. Either way, the same number of
bytes will be available if the drive is fully and accurately handled
by the ROM BIOS and operating system. Most recent and current
drives print the cylinder, head, and sectors per track information
(collectively called the drive’s geometry) on a label on the top of the
drive for easy reference during installation.
Note that all three elements of the drive geometry are actually logical,
not physical, on IDE drives. This factor explains why the geometry
can be translated (see the following), and why some IDE drives
in older machines are working, despite being installed with “incorrect”
geometries.
Use the worksheet at the end of Chapter 3, “BIOS Configurations
and Upgrades,” to record your hard drive geometry and other information
for each system you manage.
IDE Hard Drive Identification
Integrated Drive Electronics (IDE), more properly called ATA drives
(AT Attachment), are the overwhelming favorite for client PC
installations. Although SCSI hard drives (see the following) offer
benefits for network and high-performance workstation use, the
combination of constantly-improving performance, rock bottom
pricing per MB (under 1 cent and falling!), and enormous capacities
(up to 75GB and climbing) will continue to make IDE/ATA drives
the choice of most users. Figure 4.1 shows the typical IDE drive
connectors.