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).

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.

The BIOS performs a Power On Self Test (POST) for all of the different hardware components in the system to make sure everything is working properly.

The BIOS activates other BIOS chips on different cards installed in the computer. For example, SCSI and graphics cards often have their own BIOS chips.

The BIOS provides a set of low-level routines that the operating system uses to interface to different hardware devices.

The BIOS manages a collection of settings for the hard disks, clock, etc.

The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a complementary metal oxide semiconductor (CMOS) chip.

CMOS Setup provides detailed information particular to your system and can be altered as your system changes.

The BIOS uses this information to modify or supplement its default programming as needed.

Interrupt handlers

Small pieces of software that act as translators between the hardware components and the operating system.

Example, when you press a key on your keyboard, the signal is sent to the keyboard interrupt handler, which tells the CPU what it is and passes it on to the operating system.

Since the BIOS is constantly intercepting signals to and from the hardware, it is usually copied, or shadowed, into RAM to run faster.

BIOS determines whether the video card is operational.

Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card.

If they do not, there is usually video driver information on another ROM on the motherboard that the BIOS can load.

If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address.

It checks the PS/2 ports or USB ports for a keyboard and a mouse.

It looks for a peripheral component interconnect (PCI) bus and, if it finds one, checks all the PCI cards.

If the BIOS finds any errors during the POST, it will notify you by a series of beeps or a text message displayed on the screen.

Error at this point is almost always a hardware problem.

 

The BIOS then displays some details about your system. This typically includes information about the following:

Processor

Floppy and hard drive

Memory

BIOS revision and date

Display

 

 

 

 

 

BIOS looks at the sequence of storage devices identified as boot devices in the CMOS Setup.

The BIOS will try to initiate the boot sequence from the first device.

If the BIOS does not find a device, it will try the next device in the list.

If it does not find the proper files on a device, the start-up process will halt.

To enter the CMOS Setup, you must press a certain key or combination of keys during the initial startup sequence.

Most systems use "Esc," "Del," "F1," "F2," "Ctrl-Esc" or "Ctrl-Alt-Esc" to enter setup.

Normally there is a line of text at the bottom of the display that tells you "Press ___ to Enter Setup."

Once you have entered setup, you will see a set of text screens with a number of options.

"System Time/Date" - Allows you to set the system time and date

"Boot Sequence" - The order that BIOS will try to load the operating system

"Plug and Play" - A standard for auto-detecting connected devices. This should be set to "Yes" if your computer and operating system both support it.

"Mouse/Keyboard" - "Enable Num Lock," "Enable the Keyboard" and "Auto-Detect Mouse" are some of the most common options.

"Drive Configuration" - Configure hard drives, CD-ROM and floppy drives

"Memory" - Allows you to direct the BIOS to shadow to a specific memory addresses

"Security" - Set a password for accessing the computer

"Power Management" - Allows you to select whether to use power management. You can also set the amount of time for standby and suspend.

"Exit" - You always have a choice to save your changes, discard your changes or restore default settings.

Be very careful when making changes to setup.

Incorrect settings may keep your computer from booting.

When you are finished with your changes, you should choose "Save Changes" and exit.

The BIOS will then restart your computer so that the new settings take effect.

The BIOS uses CMOS technology to save any changes made to the computer's settings.

With this technology, a small lithium or Nicad battery can supply enough power to keep the data for years.

In fact, some of the newer chips have a 10-year tiny lithium battery built right into the CMOS chip!

Occasionally a computer will need to have its BIOS updated.

This is especially true of older machines.

As new devices and standards arise, the BIOS needs to change in order to understand the new hardware.

Since the BIOS is stored in some form of ROM, changing it is a bit harder than upgrading most other types of software.

Major BIOS manufacturers include:

American Megatrends Inc. (AMI)

Microid Research (MR BIOS)

Phoenix Technologies

Acerlabs

Winbond

As with changes to the CMOS Setup, be careful when upgrading your BIOS.

Make sure you are upgrading to a version that is compatible with your computer system.

Otherwise, you could corrupt the BIOS, which means you wouldn't be able to boot your computer.

Check with your computer manufacturer to be sure you need to upgrade.

EPROM: Erasable Programmable ROMs - flashed with UV light

EEPROM: Electrically Erasable Programmable ROM – flashed in situ, upgrades downloaded off vendor website usually.

BIOS is loaded into the top 64 K of the first MB of system memory

CMOS settings kept in volatile RAM (requires a battery)

Dual BIOS

Every mainboard can be destroyed through improper flashing of the BIOS, or through manual modifications of the flash file.

In such a situation, the either the BIOS cannot be loaded without errors, or invalid settings are assigned to the components.

For this reason, some manufacturers, such as Gigabyte, offer a dual BIOS function with many of their mainboards.

If the first "normal" flash BIOS is damaged, then a function built into the Gigabyte board checks to see if the BIOS starts correctly or not.

If BIOS does not start correctly, then the motherboard automatically switches over to the backup BIOS.

This gives you the possibility of overwriting the damaged flash BIOS and initiating a new startup process.

Links for upgrades, logos to replace the Energy Star symbol etc.

http://juggernaut.de/index.html

http://www.miro.pair.com/tweakbios/

http://www.xterna-net.de/~magichand/bios.htm