The BIOS is a special software usually stored on a Flash memory chip on the motherboard. It is used by the microprocessor (processor) to get the computer system started after it is turned on. It also manages data flow between the computer's operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, printer etc. When BIOS boots up (starts up) the computer, it first determines whether all of the attachments are in place and operational and then it loads the operating system (or key parts of it) into the computer's random access memory (RAM) from hard disk or diskette drive.
The BIOS uses CMOS (Complementary Metal Oxide Semiconductor) technology to save any changes made to the computer's settings. A small lithium or Ni-Cad cell, installed on the motherboard, supplies power to keep the data for years. To enter the CMOS Setup for altering custom settings of a computer, a certain key during the initial startup sequence is required to be pressed. Most systems use "Del," or "F1," keys to enter CMOS setup.
On entering CMOS setup, a text menu screen, the contents of which are different for different BIOS manufacturers, is displayed. The menu screen provides links for opening pages for changing various BIOS settings of the computer. These menus enable change of the following
The changes to CMOS setup must be made very carefully. Incorrect settings may stop the computer from booting.