BIOS
       Basic Input Output System / Support (PC)

	

	Basic Input/Output System
BIOS
ROM BIOS

    (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)