What is the difference between bios and cmos

The terms BIOS and CMOS both describe crucial components of your computer"s motherboard. They job-related together and they"re both essential, yet they are not the very same thing.

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Let"s take a look at what the BIOS and CMOS are, and also exactly how they"re various.


The BIOS (Basic Input/Output System) is firmware stored in a chip on your computer"s motherboard. It is the first program that runs once you turn on your computer system.


The BIOS percreates the POST, which initializes and also tests your computer"s hardware. Then it locates and also runs your boot loader, or tons your operating system straight.

The BIOS also gives a simple interconfront for configuring your computer"s hardware. When you start your computer system, you might check out a message prefer "Press F2 for setup." This setup is your BIOS configuration interface.


When you make transforms to your BIOS configuration, the settings are not stored on the BIOS chip itself. Instead, they are stored on a special memory chip, which is described as "the CMOS."CMOS represents "Complementary Metal-Oxide-Semiconductor." It"s the name of a production procedure offered to develop processors, RAM, and also digital logic circuits, and also is additionally the name for chips created using that procedure.

Like many RAM chips, the chip that stores your BIOS settings is made making use of the CMOS process. It holds a little amount of data, usually 256 bytes. The information on the CMOS chip contains types of disk drives are installed, the existing day and time of your system clock, and your computer"s boot sequence.

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On some motherboards, the CMOS is a sepaprice chip. However before, on the majority of contemporary motherboards, it is integrated with the RTC (real-time clock) on the southbridge.

Your BIOS memory is non-volatile: it retains its indevelopment even once your computer system has no power because your computer system requirements to remember its BIOS settings also once it"s turned off. That"s why the CMOS has its very own dedicated power source, which is the CMOS battery.

CMOS battery


The CMOS battery is a lithium-ion battery around the size of a coin. It have the right to host a charge for as much as ten years before needing to be reput. If your CMOS battery dies, your BIOS settings recollection to their defaults once your computer is turned off.


If you rotate on your computer system and your settings were reset or forgotten, your CMOS battery may be dead. For example, your hard drive may no much longer detected effectively, or your device clock may be recollection to a day in the previous, such as January 1st, 1970. If so, you deserve to replace the battery, see: How to relocation the CMOS battery.

Some motherboards, consisting of many modern-day ATX motherboards, proceed to administer power to the CMOS if the battery is reput while the computer is actively powered.

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If you want to replace your CMOS battery, make certain to consult your motherboard documentation for details and also safety indevelopment. Visit your motherboard manufacturer"s assistance webwebsite if you need to downfill a brand-new copy of your hand-operated.