BIOS (Basic Input/Output System)

BIOS

BIOS is short for Basic Input/Output System. This small program is used to startup the computer and communicate with hardware before an operating system is loaded. BIOS is stored in ROM chips on the mainboard. Some chips contain programs to support basic hardware such as parallel and serial ports, keyboard and the speaker. Another ROM chip, called the CMOS (complementary metal-oxide semiconductor) chip stores information that is subject to change such as time/date, power saving settings, and video adapter, hard drives and other device settings. BIOS settings are applied at every startup. Modern PCs copy the BIOS information to RAM for faster performance, this process is called shadowing.

Here is a picture of a common BIOS CHIP:


CMOS settings can be changed in the CMOS Setup, which can mostly be entered by pressing the DEL or F2 key during startup (depends on manufacturer, other key or key combinations might apply). Some of the most common CMOS settings are described later in this TechNote. Most mainboards have a "CMOS restore to factory defaults"- jumper which allows you to return to the default CMOS settings configured by the manufacturer. This is useful when you cannot access the CMOS Setup because of incorrect CMOS settings or lost CMOS passwords. Make sure the power is completely off when you shorten the jumper.