BIOS

What is BIOS?
BIOS or Basic Input/Output System is the first program accessed by the processor during start up to ensure that all the other basic programs, hard drives, ports, peripherals and the central processing unit are in good working condition. BIOS are different from the computer's operating system. The operating system resides in the hard drive and provides the user interface that can be seen on the screen after start up. The BIOS program, on the other hand, can be found right in a flash memory chip or ROM located in the motherboard. It is the basic requirement for booting a computer.
BIOS Functions
BIOS have several functions in a computer but its most important task is to load the operating system. BIOS provide the microprocessor its first instructions upon activating the computer. The instructions of the BIOS to the microprocessor during start up are the following: power on self test which tests the operating status of all the hardware in the computer, activation of other BIOS chips in some other computer components like SCSI and graphics cards, checking and management of computer peripherals through low level routines during the start-up process, and management of clock, hard drive and other settings.
BIOS Sequence
The usual sequence of the BIOS program during start up begins with checking the CMOS setup for any customized settings, loading the device drivers and interrupt handlers of various computer hardware, initializing power management and registers, performing the self test for power, displaying the system settings, determining the bootable devices in the computer, and initiating the boot sequence.
Changing Settings through CMOS
To change the settings in a CMOS setup, a certain key or a certain combination of keys must be pressed during the initial start up sequence. The instructions for this can usually be found at the bottom of the first screen display during the start up process. Upon entering the CMOS set up, several options are available to the user. Setting the system date and time as well as changing the boot sequence, plug and play settings, driver configurations, memory settings, password settings, and power settings are just some of the settings that can be changed on this page.
Updating BIOS
BIOS, especially on older computers, can be updated from time to time. This is so the BIOS program can recognize new devices that have just been recently manufactured. To upgrade or change a computer's BIOS, a special program from the BIOS manufacturer is needed. The BIOS update used must match the original BIOS variant.
The update is done by checking BIOS revision and date information provided on the screen during start up and comparing this with the update list in the BIOS manufacturer's website. The upgrade usually comes with a utility program but sometimes the update can be downloaded separately. This utility program and update must be copied into a floppy disk and inserted into the disk drive the next time your computer boots. This will erase the old BIOS program and install the new one.

Common manufacturers

American Megatrends

Insyde Software

Phoenix Technologies

Byosoft
POST
The computer POST (Power On Self Test) tests the computer, insuring that it meets the necessary system requirements and that all hardware is working properly before starting the remainder of the boot process. If the computer passes the POST the computer will have a single beep (with some computer BIOS manufacturers it may beep twice) as the computer starts and the computer will continue to start normally. However, if the computer fails the POST, the computer will either not beep at all or will generate a beep code, which tells the user the source of the problem.
The steps of a POST
Each time the computer boots up the computer must past the POST. The step by step procedure that a POST performs each time your computer starts is given below.
Test the power supply to ensure that it is turned on and that it releases its reset signal.
CPU must exit the reset status mode and thereafter be able to execute instructions.
BIOS checksum must be valid, meaning that it must be readable.
CMOS checksum must be valid, meaning that it must be readable.
CPU must be able to read all forms of memory such as the memory controller, memory bus, and memory module.
The first 64KB of memory must be operational and have the capability to be read and written to and from, and capable of containing the POST code.
I/O bus / controller must be accessible.
I/O bus must be able to write / read from the video subsystem and be able to read all video RAM.
If the computer does not pass any of the above tests, your computer will receive an irregular POST. An irregular POST is a beep code that is different from the standard one or two beeps. This could be either no beeps at all or a combination of different beeps indicating that the computer failed in testing POST.
BIOS SETUP
Once you have entered setup, you will see a set of text screens with a number of options. Some of these are standard, while others vary according to the BIOS manufacturer. Common options include:
System Time/Date - 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; should be set to "Yes" if your computer and operating system both support it
Mouse/Keyboard - "Enable Num Lock," "Enable the Keyboard," "Auto-Detect Mouse"...
Drive Configuration - Configure hard drives, CD-ROM and floppy drives
Memory - Direct the BIOS to shadow to a specific memory address
Security - Set a password for accessing the computer
Power Management - Select whether to use power management, as well as set the amount of time for standby and suspend
Exit - Save your changes, discard your changes or restore default settings

AMI BIOS beep codes
Beep Code Descriptions

1 short DRAM refresh failure
2 short Parity circuit failure
3 short Base 64K RAM failure
4 short System timer failure
5 short Process failure
6 short Keyboard controller Gate A20 error
7 short Virtual mode exception error
1 long, 3 short Conventional/Extended memory failure

AWARD BIOS beep codes
Beep Code Description
1 long, 2 short :-Indicates a video error has occurred and BIOS initialize the video screen to display additional information
Any other beep(s):- RAM problem.

IBM BIOS beep codes
Beep Code Description

No Beeps No Power, Loose Card, or Short.
1 Short Beep Normal POST, computer is ok.
2 Short Beep POST error, review screen for error code.
Continuous Beep No Power, Loose Card, or Short.
Repeating Short Beep No Power, Loose Card, or Short.
One Long and one Short Beep Motherboard issue.
One Long and Two Short Beeps Video (Mono/CGA Display Circuitry) issue.
One Long and Three Short Beeps Video (EGA) Display Circuitry.
Three Long Beeps Keyboard / Keyboard card error.
One Beep, Blank or Incorrect Display Video Display Circuitry.

The BIOS uses CMOS technology to save any changes made to the computer's settings. With this technology, a small lithium or Ni-Cad 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.

BIOS Troubleshooting
Because the BIOS is the essential "glue" that joins hardware to the operating system, you need to know how to deal with errors. Follow these steps to solve BIOS problems.
Incorrect CMOS Configuration
If the system can't start after a BIOS upgrade or a battery replacement, the CMOS might be corrupted. Re-enter the correct settings, save changes, and restart. An onscreen error message will usually indicate a CMOS problem. Otherwise, the settings might have been adjusted by a user. Try using the BIOS Setup auto-configure options, double-check drive configurations, save changes, and restart.
Incorrect Flash BIOS or Failed Update
If you use the wrong flash BIOS file to update your BIOS, or if the update process doesn't finish, your system can't start. You might need to contact the system or motherboard maker for service. Some BIOSes contain a "mini-BIOS" that can be reinstalled from a reserved part of the chip. Systems with this feature have a jumper on the motherboard called the "flash recovery" jumper. Micro Firmware's Web site lists popular motherboards using Phoenix BIOSes that have this feature.
To use this feature, download the correct flash BIOS, make the floppy disk, and take it to the computer with the defective BIOS. Set the jumper to Recovery, insert the floppy disk, and rerun the setup process. Listen for beeps and watch for the drive light to run during this process, because the video won't work. Turn off the computer, reset the jumper to Normal, and restart the computer.
If the update can't be installed, your motherboard might have a jumper that writes-protects the flash BIOS. Check the manual to see if your system has this feature. To update BIOS on a system with a write protected jumper, you must
1Disable the write-protection.
2.Perform the update.
3.Re-enable the write-protection to keep unauthorized people from changing the BIOS.
Summary
The BIOS contains a POST (power on self test) routine that tests memory, video, hard drives, floppy disk drives, and other important system components.
The BIOS also contains a bootstrap program that locates the operating system after the POST and transfers control to it.
The BIOS uses three methods to report errors: beep codes, onscreen error messages, and BIOS POST codes.
The BIOS contains tables of supported devices and options; the CMOS chip is used to store the options chosen with the BIOS setup program.
The CMOS chip is battery-backed.
You must verify correct floppy disk drive and hard drive configurations before a system can be started. These settings are found in the standard CMOS setup screen.
By making adjustments to other BIOS screens, you can adjust the performance of the system, configure the system for compatibility with Windows PnP-compatible boards, adjust or disable built-in ports, and control power management.
A BIOS needs to be upgraded when you want to use new hardware, new software, or new features not included in the current BIOS.
BIOS upgrades can be performed with software (flash BIOS) or by replacing the chip.