Your computer stores low-level settings such as system time and hardware settings in its CMOS. These settings are configured in the BIOS or UEFI setup menu. If you’re having hardware compatibility issues or other issues, you may want to try clearing the CMOS.
Clearing CMOS will reset your BIOS or UEFI settings to factory defaults. In most cases, you can clear CMOS from the BIOS menu or by pressing the CMOS button on the back. In some cases, you may need to open the computer case.
Using the BIOS or UEFI menu
The easiest way to clear CMOS is through the computer’s BIOS or UEFI setup menu. To access the setup menu, restart the computer and press the key that appears on the screen (usually Delete or F2) to access the setup menu.
related: What is UEFI and how is it different from BIOS?
Consult your computer manual if you do not see the keys displayed on the screen. Different computers use different keys. (If you build your own computer, see your motherboard manual.)
If you’re running Windows 8, Windows 10, or Windows 11, you may be able to access the BIOS or UEFI from Windows itself.
In the BIOS, look for the Reset option. It may be named “Reset to Defaults”, “Load Factory Defaults”, “Clear BIOS Settings”, “Load Settings Defaults” or something similar.
Use the arrow keys to select it, press Enter, and confirm the action. If you’re using a computer with UEFI instead of BIOS, you might be able to use a mouse.
Your BIOS or UEFI will now use its default settings – if you’ve changed any settings in the past, you’ll have to change them again.
Press the Clear CMOS button
Newer motherboards, especially the more expensive ones designed for enthusiasts, often have a special button to clear the CMOS.
The button can be located on the back of the motherboard, near all ports, or inside the chassis of the motherboard itself. The manual that came with your computer or motherboard will tell you exactly where to find it.
notes: Do not confuse the CMOS clear button with the BIOS button. The BIOS button allows you to flash the BIOS without a CPU installed on the motherboard, revert to a previous BIOS version if the BIOS update fails, or both.
Once you find the CMOS clear button, press it for about 10 seconds. You may need a paper clip — the CMOS clear buttons near the ports on the back are usually recessed so they can’t be accidentally pressed.
CMOS buttons on motherboards are usually clearly marked, and they are usually not recessed. You still need to hold it down for a few seconds to trigger the reset.
Using CLEAR CMOS motherboard jumpers
Many motherboards include a jumper that can be used to clear the CMOS settings if your BIOS is inaccessible. This is especially useful if the BIOS is password protected and you do not know the password, or if you have made changes that prevent you from accessing the BIOS normally.
The exact location of the jumpers can be found in the motherboard (or computer) manual. If you want to use motherboard jumpers, you should consult the manual for more detailed instructions.
However, the basic process is very similar on all computers. Flip the computer’s power switch to the off position to make sure it is not receiving any power. Open the computer case and find the jumper called CLEAR CMOS, CLEAR, CLR CMOS, PASSWORD or CLR PWD – it’s usually located near the CMOS battery mentioned below.
hint: The CMOS clear jumper almost always has three pins.
Make sure you are grounded to avoid static damage to the motherboard before touching it. Set the jumper to the “clear” position, power on the computer, power it off again, set the jumper to the original position – and you’re done.
Reinstall the CMOS battery
If your motherboard doesn’t have a CLEAR CMOS jumper or button, you can usually clear its CMOS settings by removing the CMOS battery and replacing it. The CMOS battery provides the power used to save BIOS settings — that’s how your computer knows how much time has passed, even if it’s been off for a while — so removing the battery removes power and clears the settings.
notes: Not all motherboards have removable CMOS batteries. If the battery won’t come loose, don’t force it.
First, make sure your computer is powered off and grounded to prevent static electricity from damaging the motherboard. Locate the round flat silver battery on the motherboard and carefully remove it. Wait five minutes, then reinstall the battery.
Clearing CMOS should always be done for some reason – such as to fix a computer problem or clear a forgotten BIOS password. If all is well, there is no reason to clear the CMOS.