The CMOS settings maintain fundamental system configuration
information, which is stored in a special chip on the motherboard.
This chip, usually powered by a battery, can operate independently
of the rest of the computer. It keeps things like the system clock
up-to-date even when the power is switched off.
The CMOS settings also record what sort of disks are installed
in the PC, whether or not a password is required at start-up, and
which devices (e.g. floppy, hard disk, CD-ROM or network) should be
used when trying to boot up the computer. If your CMOS settings are
inaccurate, then your computer may not work properly.
Some viruses and trojans, such as Troj/KillCMOS-E,
deliberately corrupt these settings to try to stop your computer
working. Although it is usually fairly easy to correct the CMOS
settings, the procedure for doing so varies from computer to
computer. You may need to refer to your computer's manual or the
manufacturer's website for assistance.