BIOS

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)