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The Hardware BIOS

What is the BIOS?

BIOS stands for Basic Input Output System and it is a small program and memory area, held in semi-permanent memory on the motherboard. There are two main parts to this:

  • An area holding the basic hardware configuration. This is normally held in CMOS memory (-so it can be changed), and the contents are maintained by power from the silver-oxide battery on the motherboard. If this battery is removed - or dies - then this information is all lost and the BIOS will revert to it's defaults

  • Basic programs to:

    • Execute the Power On Self Test (POST), which checks all the hardware components prior to allowing access to the BIOS Setup. If any errors are found, they are displayed to the user (-or communicated by a number of beeps, in case the problem is with the display system) and the BIOS halts. The only way past this is to identify the problem, fix it and reboot

    • Allow the user to view and alter the stored hardware configuration data (-aka BIOS Setup) if a particular key is pressed prior to the initiation of the boot sequence. The window of opportunity is slight so you need to watch the screen for the prompt (-which is normally displayed on the BIOS splash page)

    • Once the POST is complete, the BIOS transfers control to any program identified in the boot sector on one of the available drives. For machines running Linux, this will be a version of the GRUB loader

    These are normally stored in Flash memory and can be updated (-or flashed) if required (-normally, this would be only if problems are encountered)

Types of BIOS

BIOS programs are not normally directly written by the motherboard manufacturer: virtually without exception, they are instead licenced from one of the dedicated BIOS producers, normally one of the following three:

  • American Megatrends Inc (AMI BIOS)
  • Award
  • Phoenix

The BIOS provided by each manufacturer all look slightly different, but all provide similar functionality. For example, they all use a text based menu system to view and edit the hardware configuration data but the look and feel is (slightly) different in each - as is the key pressed to enter the setup program: for example, in AMI BIOS, it is entered by pressing the "Delete" key.

The Hardware Configuration Database

These days, each BIOS has pretty good support for automatically detecting the hardware installed in a system. This means that very little change needs to be made to the default hardware configuration, even when building a new PC. The BIOS now has the capability to detect exactly which CPU, chipset, drives, memory, etc, are connected to the PC, so many users will just be able to run their PC, directly out of the box, without ever having to enter the BIOS Setup program.

The only reason, then, to alter the default configuration, is if you need to tweak performance or deal with some errant piece of hardware. Examples are:

  • If dual-booting with Windows XP, you may need to configure the Drives to use IDE mode and not the newer AHCI mode, which XP does not seem to support

  • You may need to update the boot order to identify the correct drive(s) to search for a bootable O/S (-in Linux, this would be the device where the /boot filesystem resides)

  • If you feel confident enough to extract a few more cycles from your processor, you can change the CPU settings and try overclocking by overriding the default CPU settings

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