BIOS has several functions in a computer but its most important task is to load the operating system. BIOS provides the microprocessor its first instructions upon activating the computer. Some of the common tasks that the BIOS performs include:
A power-on self-test (POST) for all of the different hardware components in the system to make sure everything is working properly. During this process, the BIOS checks a specific memory location (address) on the computer (0000:0472). Information on whether the computer is being started from an off position (cold boot) or from a restart (warm boot) is stored at this location.
Activating other BIOS chips on different cards installed in the computer like SCSI and graphics cards that often have their own BIOS chips.
Providing a set of low-level routines that the operating system uses to interface to different hardware devices – It is these routines that give the BIOS its name. They manage things like the keyboard, the screen, and the serial and parallel ports, especially when the computer is booting.
Retrieves information from CMOS (complementary metal-oxide semiconductor; a battery operated memory chip on the motherboard that stores time, date, and critical system information). If necessary, the BIOS tailors its startup routine to match changes to CMOS.
The first thing the BIOS does is check the information stored the RAM located on a complementary metal oxide semiconductor (CMOS) chip. The 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 are small pieces of software that act as translators between the hardware components and the operating system. For 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. The device drivers are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive and floppy drive. Since the BIOS is constantly intercepting signals to and from the hardware, it is usually copied, or shadowed, into RAM to run faster.