BIOS - Upgrading and Repairing PCs - page 276

CMOS is stored because the CMOS configuration and setup programs typically are part of the BIOS.
This is another example of how close the relationship is between the BIOS and the motherboard
hardware.
Backup programs and utilities are available in the public domain for CMOS RAM information, which
can be useful for saving and later restoring a configuration. Unfortunately, these programs are BIOS
specific and function only on the BIOS for which they are designed. As such, I don't usually rely on
these programs because they are too motherboard and BIOS specific and do not work on all my
systems seamlessly.
Table 5.2 shows the values that might be stored by your system BIOS in a special CMOS byte called
the diagnostic status byte . By examining this location with a diagnostics program, you can determine
whether your system has set trouble codes, which indicate that a problem previously has occurred.
Table 5.2. CMOS RAM Diagnostic Status Byte Codes
If the diagnostic status byte is any value other than 0 , you typically get a CMOS configuration error on
bootup. You can clear these types of errors by rerunning the setup program.
Preboot Environment
Some systems use the Phoenix BIOS preboot environment, which has a graphical user interface (GUI)
that allows a user to access the BIOS Setup, extended diagnostics, a backup/restore application, or a
full recovery of the original system contents (product restoration to factory-delivered contents). All
these applications (except the BIOS Setup) are stored in the HPA (Host Protected Area) , a hidden
area of the hard drive literally situated past the reported end of the drive. The number and type of
applications accessible via the preboot environment depend on which options the OEM selected
when designing the system. Figure 5.6 shows the IBM/Lenovo implementation of the Phoenix BIOS
preboot environment. This environment is activated by pressing the Enter key on the keyboard during
the POST.