BIOS

BIOS – Basic input/output system is the code the computer executes when it first turns on.  The BIOS initializes system devices such as the video card, various storage drives like the hard drive, DVD drive, and floppy drive, and other hardware.  Once the operating system takes control of the computer, BIOS still functions to control hardware devices.

Engineers refer to this process as bootstrapping, from the concept of people pulling themselves up by their bootstraps.  Computers boot by running one set of instructions, the BIOS, in preparation of running other programs such as word processing applications, web browsers, servers and other software and services.

In the early days of PC's, they stored their BIOS on ROM chips.  Some hardware devices had their own extended BIOS, stored on their own ROM.  These included some hard drives and video cards.  A small battery powered the ROM chips, called CMOS RAM.  They required very little power to operate, so the small system battery provided enough power to maintain data.   

Later, EEPROM, a form of non-volatile storage ROM (meaning it retains data even without power,) began taking the job of storing the BIOS.  EEPROM, and flash memory that came into prominence in 1995, are both re-writable.  EEPROM and flash memory work without power.  So now the computer battery does nothing but power the system clock.  When developers find bugs in the BIOS, or users update hardware, they “flash” their BIOS, updating it with the latest version.

Modern PC's contain a number of BIOS chips.  The motherboard BIOS initializes basic computer functions and peripherals such as the keyboard, USB devices, and storage devices.  Just as in the old days, other hardware devices hold their own BIOS chips. 

• When the computer uses them prior to loading the operating system
• When the system BIOS can't handle the complex instructions that manage the hardware

Modern operating systems have their own device drivers.  But they still rely on the BIOS for certain tasks such as initializing a device. 

Companies such as American Megatrends develop and license generic motherboard BIOS cores.  Motherboard manufacturers customize this BIOS core for their motherboard.  When users need to update the BIOS, they therefore turn to the motherboard manufacturers.

Modern BIOS's produce beep codes through the motherboard speakers.  These codes signify different errors or states.  American Megatrends provides a list of beep codes on their web site:  http://www.ami.com/support/doc/AMIBIOS8_Checkpoint_and_Beep_Code_List_PUB.pdf

These codes include:

• 3 Beeps – Base memory write test error.  Reseat or replace bad modules with good ones.
• 7 Beeps – Exception error, a possible major motherboard problem.  Check add-in cards for problems.
• 8 Beeps – Display memory error.  For motherboard with built in video adapters the user replaces the motherboard or disables the video adapter, replacing it with an add-in card.  For add in cards the user replaces the video adapter.

A new project called Coreboot seeks to replace BIOS firmware with a more lightweight system that performs fewer tasks before passing control to modern operating systems.  This is a public project licensed under the GNU General Public License. Many individuals and corporations contribute to this project, including AMD and MSI.  For more information visit Coreboot's web site at http://www.coreboot.org/Welcome_to_coreboot.