BIOS is the first program executed once you turn on your microcomputer. It is stored in read-only memory (ROM) and since ROM is nonvolatile, BIOS is not erased when power goes off. Major BIOS providers are American Megatrends Incorporation (AMI) and Phoenix Technologies. The first thing BIOS does is to read data values stored in a special, tiny RAM chip powered by a battery that can go on for years. These data provide date and time, computer-accessing password, and settings that affect BIOS operation. These data can be changed by entering the setup mode once you turn on your computer. On most computers you enter setup mode by pressing the Esc, Del, F1, or F2 key. Basic BIOS tasks are as follows:

- Loading the operating system into memory. This is referred to as the booting process and it is BIOS’s most important task.

- Providing special pieces of software that the operating system uses to interface to basic input/output hardware devices such as the keyboard, mouse, and monitor. These programs are called device drivers and this is the task that gives BIOS its name.

- Providing a power-on self-test (POST) that checks the proper functioning of the different hardware components.