BIOS

BIOS(Basic Input Output System) BIOS is software stored in a ROM (read only memory) chip located in the motherboard of a PC. It is the first code run when the computer is turned on. When you start your computer, the CPU (Central Processing Unit), sends control of the PC to the BIOS routine. After the CPU gives the BIOS the "go ahead", it begins looking for all the components and peripheral devices attached to your computer. The CMOS memory chip (complementary metal oxide semiconductor) stores the data that is used by the BIOS setup and testing routines^[1]. When the computer is turned on(or booted) the BIOS runs a set of routines that tests the hardware, starts the operating system, and supports the transfer of data between hardware devices at startup. In most PCs, the BIOS has 4 main functions.

1. POST - Tests computer hardware, ensuring hardware is properly functioning before starting process of loading operating system.

2. Bootstrap Loader - Process of locating the operating system. If capable operating system located, BIOS will pass the control to it.

3. BIOS - Software and drivers that interface between the operating system and your hardware. When running DOS or Windows you are using complete BIOS support.

4. BIOS / CMOS Setup - Configuration program that allows you to configure hardware settings including system settings such as computer passwords, time, and date^[2].

While running the POST (power on self test) if any fatal errors occur the boot process stops. A sequence of beeps will sound which identifies where the problem is. Below is an example of what those beeps may mean depending on the manufacturer of the bios software^[3].

Number of Beeps	Description of Problem	Solution
1 beep	DRAM refresh failure	Try re-seating the memory first. If the error still occurs, replace the memory with known good chips.
2 beeps	Parity Circuit Failure
3 beeps	Base 64K RAM failure
4 beeps	System Timer Failure	Send System Board in for Repair
5 beeps	Processor Failure
6 beeps	Keyboard Controller / Gate A20 Failure	Try re-seating the keyboard controller chip. If the error still occurs, replace the keyboard chip. If the error persists, check parts of the system relating to the keyboard, e.g. try another keyboard, check to see if the system has a keyboard fuse
7 beeps	Virtual Mode Exception Error	Send System Board in for Repair
8 beeps	Display Memory Read/Write Failure	Indicates a memory error on the video adapter. Try re-seating the video card. If it still beeps, try replacing the video card or the memory on the video card
9 beeps	ROM BIOS Checksum Failure	Indicates faulty BIOS chip(s). It is not likely that this error can be corrected by re-seating the chips. Consult the motherboard supplier or an AMI product distributor for replacement part(s)
10 beeps	CMOS Shutdown Register Read/Write Error	Send System Board in for Repair
1 long 2 short	Video failure	Reseat the video board - replace if board is determined to be faulty
1 long 3 short	Video failure
1 long	POST passed	No Errors

Example BIOS User Interface

Example BIOS chip