CMOS?

Here's a good demonstration of CMOS memory theory:
http://tech-www.informatik.uni-hamburg.de/applets/cmos/cmosdemo.html

complementary metal oxide semiconductor.

CMOS is the component/technology frequently used to store the BIOS. The BIOS is A Set of Machine Language instructions used to tell the mother board such things as how to talk to and start up from a floppy disk, CDROM, or hard Drive. How to read how much and what kind of memory is available to the system is another example.

Short for complementary metal oxide semiconductor. Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. This makes them particularly attractive for use in battery-powered devices, such as portable computers. Personal computers also contain a small amount of battery-powered CMOS memory to hold the date, time, and system setup parameters.