What's the difference between BIOS and CMOS?

Many people use the terms BIOS (basic input/output system) and CMOS (complementary metal oxide semiconductor) to refer to the same thing. Though they are related, they are distinct and separate components of a computer. The BIOS is the program that starts a computer up, and the CMOS is where the BIOS stores the date, time, and system configuration details it needs to start the computer.

The BIOS is a small program that controls the computer from the time it powers on until the time the operating system takes over. The BIOS is firmware, which means it cannot store variable data.

CMOS is a type of memory technology, but most people use the term to refer to the chip that stores variable data for startup. A computer's BIOS will initialize and control components like the floppy and hard drive controllers and the computer's hardware clock, but the specific parameters for startup and initializing components are stored in the CMOS.

Also see:

• On a Compaq computer, how do I access BIOS Setup?
• What is a CMOS battery, and why does my computer need one?
• On a PC, how do I reset or remove the CMOS password?
• If my computer beeps and fails to boot, what do the beeps mean?
• How do I enter the Setup program in my BIOS?
• With my Dell OptiPlex GX150, why should I upgrade from A05 BIOS to A06 BIOS?