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Redirected from: PC BIOS

Definition: BIOS


(Basic Input Output System) A set of routines residing in firmware that boots (starts) the operating system and sets up the hardware in a Windows PC. Users can change setting in the BIOS; for example, to boot from a flash drive before booting from the internal storage drive (see first boot sequence).

Prior to using Intel chips, the Mac had a startup counterpart, but it was never made as public as the BIOS for PCs. Starting in the mid-2000s, the Unified Extensible Firmware Interface (UEFI) began replacing the BIOS system (see UEFI). However, many people refer to UEFI as the BIOS and "UEFI BIOS" is also a common designation.

Basic Peripheral Support
Prior to loading the operating system, the BIOS identifies software drivers for peripheral support, including keyboard, mouse, monitor and storage drive. After the OS is loaded, more elaborate drivers typically 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 dates back to the first IBM PC in 1981 and used to be permanently stored on a read-only memory (ROM) chip. Adding a peripheral with a 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 peripheral devices.






BIOS Identification
TouchStone Software's BIOS Wizard tested a PC's BIOS to see if it needed updating. This example dates back to the days of floppy disks. (Image courtesy of TouchStone Software Corporation.)