BIOS Last modified: Tuesday, July 29, 2003
Pronounced "bye-ose," an acronym for basic input/output system. The
BIOS is 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). Additional DOS functions
are usually added through software modules. This means you can upgrade to a
newer version of DOS without changing the BIOS.
PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP
BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash
memory rather than ROM.
Cheers Doug
