BIOS and CMOS

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Basic Input/Output System (BIOS)

The BIOS runs at the startup sequence where it configures devices (including keyboard, display screen, disk drives, and serial communications) and then boots the operating system. The function of the BIOS is so vital that the information on the BIOS is stored on a chip separate from the hard drive to protect it from potential crashes.

To access the BIOS interface, look for instructions as soon as the computer is turned on. Many systems require users to press any of the following keys: F2, F8, F10, or F12 immediately after turning on the computer. Once the interface loads, users can change the system date and time, alter the boot sequence, and manage hardware components.

It is often necessary to edit the boot sequence to allow for booting from a Live operating system, such as a CD or DVD, or when installing an operating system for the first time. In that case, the CD/DVD option should be set at the top of the sequence and the corresponding media should be inserted before boot.

Complimentary Metal Oxide Semiconductor (CMOS)

A chip mounted on the motherboard of a computer that runs the BIOS using extremely small amounts of energy from a battery which is also mounted on the motherboard.

Replacing the CMOS Battery

The CMOS battery is a watch battery that is connected and secured right on the motherboard. Eventually, the CMOS battery may begin to fail or lose its charge, and this may be evidenced when your computer is seeming to "lose time" on your desktop (the clock will slow down).

To remedy this, open up the tower or case and locate the CMOS battery, it will be the only watch-sized battery on the mother board. Some batteries will directly pop out, others can be disconnected by popping a lever. Replace with similar watch-sized battery (type of battery depends on the model of the computer/motherboard).

Passwords placed on the BIOS preventing the user from altering settings can be replaced by disconnecting and reconnecting the CMOS battery.