processors always look for the start of the BIOS to be in this location in memory. After
the processor loads the BIOS programs from this location, the system boot sequence starts.
As I’ve discussed earlier, there are several BIOS programs in a PC. In addition to the
system BIOS, there are BIOSs to control the peripheral devices that have been added to the
computer. For example, most video cards, hard disks, and SCSI adapters have a BIOS that
controls parts of their interaction with the processor and other motherboard components.
Older 16-bit computers use a technique calledROM shadowingto speed up the boot
process. Because ROM chips have a very slow access speed (150 nanoseconds), the BIOS
stored on the ROM is copied into the system memory and the ROM’s address is adjusted
to point to the BIOS’s new location. This allows the computer to work with the faster
RAM and bypass the slower ROM. Newer 32-bit or higher PC systems load special 32-bit
device drivers into RAM during system startup, which allows them to bypass the slower
16-bit ROM code.The BIOS Configuration
Most computers purchased today are shipped directly from the factory already set up
and configured. When you buy a PC online, over the phone, or at the local computer
reseller, it has all of its components installed and the system configuration and setup
is already completed. There is usually very little need for you to ever change your BIOS
orconfigurationdatasettings.Itisreasonabletoexpectthatacomputeruserwouldnever
press theDELkey during the boot sequence to open their system setup and change the
PC’s configuration.
However,itisalsopossiblethatatsomepointyoumayneedtoreviewormodifyyour
PC’s setu pand configuration information. When that time comes, you will need an un-
derstanding of the information and configuration data stored by the BIOS setu p program
in its configuration data. This section covers the information you’ll need if you ever have
to run the setup program and change the configuration data.System Configuration Data
The hardware configuration of the computer is stored in the computer’s CMOS memory.
This data is managed through the BIOS’ setu p program. This section discusses how to
access the setup program and each of the menu types it displays.Setup Program
Each BIOS program will tell you how to gain access to its setup program. Right after it
finishes the POST, the BIOS displays the key you press to start the BIOS setup program
and gain access to the configuration information. An example of this display is shown
in Figure 6-3. The keystrokes used to access the setup program for most of the popular
BIOS are listed in Table 6-5.
The BIOS setu p program stores the hardware configuration of a PC in CMOS mem-
ory. What configuration data is included depends on the processor and BIOS in use.Chapter 6: The BIOS and the Boot Process^121