CMOS RAM

The Complementary Metal-Oxide Semiconductor (CMOS) is the area where the computer stores its configuration information, such as whether or not the computer has a floppy drive, the amount of memory installed, the date and time for the system, and the number and size of the hard drives that are installed. Think of the CMOS information as an inventory list for the majority of components that are installed on the computer.

Remember
CMOS is the computer's inventory list. It tells the computer which devices reside in the system. For example, the CMOS information lists your hard drive, floppy drive, and other information - such as the date and time for the system.

Where is the CMOS information stored? Is the CMOS information stored in the BIOS chip, or perhaps another ROM chip? The answer is neither. In fact, if the information were stored in a ROM chip, you wouldn't be able to go into the CMOS setup program and change the configuration. The CMOS configuration information is stored in a type of RAM called CMOS RAM.

CMOS RAM is a special, volatile RAM chip that stores the CMOS information. Volatile means that if power is lost, the information is wiped out. This could present a problem with regard to CMOS configuration because if the CMOS RAM is wiped out, the computer forgets its inventory information and has to relearn it. Thus, the computer has a small battery on the motherboard that maintains enough of a charge to avoid CMOS RAM losing its data.