from
The Free On-line Dictionary of Computing (8 July 2008)
Basic Input/Output System
BIOS
ROM BIOS
<operating system> (BIOS, ROM BIOS) The part of the {system
software} of the {IBM PC} and compatibles that provides the
lowest level interface to {peripheral} devices and controls
the first stage of the {bootstrap} process, including
installing the {operating system}. The BIOS is stored in
{ROM}, or equivalent, in every PC. Its main task is to load
and execute the operating system which is usually stored on
the computer's {hard disk}, but may be loaded from {CD-ROM} or
{floppy disk} at install time.
In order to provide acceptable performance (e.g. for screen
display), some software vendors access the routines in the
BIOS directly, rather than using the higher level operating
system calls. Thus, the BIOS in the compatible computer must
be 100% compatible with the IBM BIOS.
As if that wasn't bad enough, many {application programs}
bypass even the BIOS and address the screen hardware directly
just as the BIOS does. Consequently, {register} level
compatibility is required in the compatible's display
electronics, which means that it must provide the same storage
locations and identification as the original IBM hardware.
(1999-06-09)