CMOS

Also known as a Real Time Clock (RTC), Non-Volatile RAM (NVRAM) or CMOS RAM, CMOS is short for Complementary Metal-Oxide Semiconductor. CMOS is an on-board semiconductor chip powered by a CMOS battery inside computers that stores information such as the system time and system settings for your computer. A CMOS is similar to the Apple Macintosh computer's PRAM. To the right is an image of a CMOS battery on a computers motherboard and the most common CMOS battery you're likely to encounter with your computer.

To the right is some examples of other types of batteries that may be used in a computers to power the CMOS memory. As mentioned above the most common type of battery is the coin cell battery (lithium battery), usually about the size of a U.S. Nickel.

The standard lifetime of a CMOS battery is around 10 Years. However, this amount of time can change depending on the use and environment that the computer resides.

Information about entering CMOS setup can be found on document CH000192.
See our CMOS help page for additional help and support information about the CMOS.

Also see: BIOS, MOS, Motherboard definitions, PRAM, Quartz crystal, RTC

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