Geek Speak: What’s a CMOS?

If you work around computers long enough, you may run across the acronym CMOS (it stands for complementary metal-oxide semiconductor, but that’s not really important to remember). CMOS can sometimes be mentioned in error screens when a computer doesn’t start properly. In that case, it refers to a tiny amount of memory powered by a small coin-size battery. Have you ever wondered how your computer can keep correct track of time, even when the power cord or primary battery is unplugged? The answer is the CMOS battery. In very old computers (~10 years) or computers that often have their power supply turned off, you may see a CMOS error screen. In that case, spending a few dollars on a new CMOS battery usually clears up the error!