BIOS (Basic Input Output System)

BIOS stands for Basic Input Output System. It is defined as a firmware that controls much of the computer´s input/output functions such as communication with disk drives, the printer, RAM chips and the monitor. It is a set of software instruction parameters that are hard coded into a chip. These instruction parameters within BIOS versions have changed as technology has developed in regard to hardware. The BIOS is typically placed on 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. Most 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 standardized, so all PCs are alike 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. The POST      Power On Self Test is the first instruction executed during start-up. It checks the PC components and that everything works. You can recognize it during the RAM test, which occurs as soon as you turn power on.      You may follow the checks being executed in this order, as the information are gathered: Information about the graphics adapter Information about the BIOS (name, version) Information about the RAM (being counted)      As users, we have only limited ability to manipulate the POST instructions. But certain system boards enable the user to order a quick system check. Some enable the user to disable the RAM test, thereby shortening the duration of the POST. The duration of the POST can vary considerably in different PCs. On the IBM PC 300 computer, it is very slow. But you can disrupt it by pressing [Esc].      Error messages      If POST detects errors in the system, it will write error messages on the screen. If the monitor is not ready, or if the error is in the video card, it will also sound a pattern of beeps (for example 3 short and one long) to identify the error to the user. If you want to know more of the beeps, you can find explanations on the Award, AMI and Phoenix web sites. For instance you will receive error messages if the keyboard is not connected or if something is wrong with the cabling to the floppy drive. AMI BIOS Phoenix / Award BIOS MR BIOS

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Last Update: 10:58 PM 11/15/01