Intel-based computers have had a watch battery attached to the motherboard since the first 286s rolled off the assembly lines nearly 30 years ago. The CMOS battery serves several important functions. This small battery that is attached to the motherboard can be accessed by removing the cover on most computers.
Keeps the System Date and Time
The CMOS battery stores the system time and settings that most be loaded when you turn the system on. Older computers reset to a date of 1-1-1980. Computers running Windows XP or later will set the system date to the date of the last saved system restore point.
Allows System Settings to be called up
A few additional settings are stored by the system. The CMOS battery allows these settings to be loaded into system memory when the computer boots.
Why does it look like a watch battery?
The CMOS battery is a standard-size watch battery in most desktop systems. The user can buy a replacement at any place that sells watches.
How long does this battery last?
CMOS batteries can last for 5 years. If a computer's CMOS battery loses a charge, you will have to manually set the system date and time.
What does CMOS stand for?
CMOS is the acronym for Complementary Metal Oxide Semiconductor.