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.