basic input/output system
The BIOS is what's coded into a PC's ROM to provide the basic instructions for controlling system hardware. The operating system and application programs both directly access BIOS routines to provide better compatibility for such functions as screen display. Some makers of add-in boards such as graphics accelerator cards provide their own BIOS modules that work in conjunction with (or replace) the BIOS on the system's motherboard.
See also: ROM