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(computer science)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


This article is provided by FOLDOC - Free Online Dictionary of Computing (


(Basic Input Output System) A set of routines residing in firmware that boots the operating system and sets up the hardware in an x86-based PC. In newer computers, the UEFI is used as the startup system and not the BIOS (see UEFI).

Prior to loading the operating system, the BIOS provides software drivers for the basic peripheral support that is part of the motherboard, including the keyboard, mouse, monitor and hard disk. The drivers enable the user to edit configuration settings and allow the hardware to boot from the hard disk or other storage device.

After the operating system is loaded, more elaborate drivers are typically loaded, which replace the BIOS routines. The BIOS also supports internal services such as the real-time clock (time and date).

The BIOS Sets Up the Computer
On startup, the BIOS tests the computer and prepares it for operation based on the installed hardware and settings, which are user configurable. For example, it initializes RAM and the devices on the PCI bus. The BIOS searches for extensions on bootable peripherals (see OPROM) and sets up pointers in RAM to access those routines (see interrupt vector). It then loads the OS and passes control to it.

From ROM BIOS to Flash Memory
The BIOS, which dates back to the first IBM PC in 1981, used to be permanently stored on a read-only memory (ROM) chip. Adding a peripheral with a brand new technology often required a chip change. Later, the BIOS was stored in updatable flash memory. See BIOS setup, BIOS upgrades, beep codes and UEFI.

BIOS Interaction
On startup, the BIOS provides the routines necessary to test and configure the hardware and use the peripheral devices included on the motherboard.

BIOS Identification
TouchStone Software's BIOS Wizard is a nifty utility that identifies and tests your PC's BIOS to see if it needs to be updated. The program is available at (Screen image courtesy of TouchStone Software Corporation,
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