(bī´ōs) Acronym for basic input/output system, the built-in
software that determines what a computer can do without
accessing programs from a disk. On PCs, the BIOS contains all
the code required to control the keyboard, display screen, disk
drives, serial communications, and a number of miscellaneous
functions. The BIOS is typically placed in a ROM chip that comes
with the computer (it is often called a ROM BIOS). This ensures
that the BIOS will always be available and will not be damaged
by disk failures. It also makes it possible for a computer to
boot itself. Because RAM is faster than ROM, though, many
computer manufacturers design systems so that the BIOS is copied
from ROM to RAM each time the computer is booted. This is known
as shadowing. Many modern PCs have a flash BIOS, which means
that the BIOS has been recorded on a flash memory chip, which
can be updated if necessary. The PC BIOS is fairly standardized,
so all PCs are similar at this level (although there are
different BIOS versions). Additiona