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what is BIOS
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 Pronounced "bye-ose," an acronym for basic input/output system. The BIOS is built-in software that determines what a computer can do without accessing programs from a disk. On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions.

The BIOS is typically placed in a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and will not be damaged by disk failures. It also makes it possible for a computer to boot itself. Because RAM is faster than ROM, though, many computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing.

Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.

The PC BIOS is fairly standardized, so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.

PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory rather than ROM.

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'BIOS' is also used when referring to BIOS setup utility which is a program on that very chip. You can run (or access) that program even if you don't have any disk drives attached. It is usually done by pressing a hotkey when you start your computer. Different BIOSes have different hotkeys for accessing setup utility. For example Award uses DEL, Phoenix uses F2 (Note: recently they merged so I don't know what's the hotkey on the new Award/Phoenix BIOS).

What you can do in BIOS setup utility is:
- set your system's date
- define your IDE hard disk and floppy drives
- configure RAM settings (such as timings)
- configure power management
 and sometimes also:
- low level format your hard drives
- configure onboard peripheral devices (audio/video etc)

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