CMOS – Complementary metal oxide semiconductor

CMOS is a battery powered semi conductor chip on the motherboard. CMOS is used to store system clock, hardware and system settings. It is a very small memory and is non volatile. CMOS is used to store BIOS settings. BIOS settings include the system hardware settings, system clock.

NOTE: CMOS in computers is different from CMOS sensor. CMOS sensor is used in digital cameras to convert images into digital data.

Few other things about CMOS

CMOS and BIOS are two different things that work together. CMOS is a small chip powered by CR2032 cell referred to as CMOS battery. CMOS is also called with other names that are, Real-Time clock, Non volatile RAM, non volatile BIOS memory, CMOS RAM.


CMOS is a small memory chip on a motherboard.. But it will lose all the data when power supply is switched off. So to make it non volatile, CMOS is powered by a CMOS battery that is a small CR2032 cell, This cell provides power to the CMOS continuously for many years.

When you start your computer BIOS checks the system settings from the CMOS chip and help in checking all the hardware and loading the Operating system.

CMOS battery

CMOS battery is a small CR2032 cell. It has its place on the motherboard in a desktop computers. It is a round button type cell and can be easily located and replaced. CMOS battery can provide power to CMOS for around 10 years, but in some cases it won’t last 10 years.

You can easily check if the CMOS battery is dead or not. When you start your computer, if your computer doesn’t show correct date and time each time you start your computer than you need to change the CMOS battery because it is dead. Loss of BIOS settings is also a sign of a dead CMOS battery.

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BIOS – Basic Input/Output System

RAM – Random Access Memory

HDD – Hard disk Drive

SSD – Solid State Drive


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