How to Reset Your CMOS and Why You Might Need To

The CMOS, also known as the Complementary Metal-Oxide-Semiconductor, is a small chunk of memory used to store your computer’s BIOS or UEFI configuration. This configuration controls what your computer does on boot. If you’ve mangled your BIOS with a failed overclocking setup or your machine won’t boot properly, returning the BIOS or UEFI to the factory defaults can often set things right. You will lose any custom BIOS configurations, but those can typically be easily reset. If you have an especially complicated setup, you can often backup your working UEFI settings and restore later. You might not have one now, but it’s a good procedure for the future.

If you’ve built your own computer, it should be easy to reset your CMOS. Pre-built systems might be a little more picky, but you can normally make one of the methods below work for you.

Note: for the sake of brevity and recognition, we will use the term “BIOS” below to refer to UEFI and BIOS firmware.

If you see a button on your computer’s case labelled “Clear” or “Reset,” that will reset the CMOS.

1. Turn off your computer.

2. Disconnect your computer from the wall outlet. You can unplug the power from the back of your power supply or from the wall outlet.

3. Locate the case button labelled “Clear” or “Reset.” It’s typically next to or near the power button.

cmos-reset-case-reset-button

4. Hold the “Clear” or “Reset” button down for five to ten seconds, then release it. You might need to use the end of a pen to hold down the button if it’s small.

5. Reconnect your computer to power and reboot.

6. Press the correct key to enter your BIOS options. On most motherboards this is the “Delete” key, except for ASRock motherboards which use “F2.”

7. Adjust your BIOS options as necessary. Some motherboards have the option to load “optimized defaults” which are a great starting point.

Some higher-end motherboards have a board-mounted button to reset the CMOS. This can be accessed by opening the computer case and locating the button within the case. It will typically be labelled something like “CLR,” “CLEAR” or “RESET.”

1. Turn off your computer.

2. Press the case’s power button multiple times to discharge any motherboard capacitors.

3. Disconnect your computer from the wall outlet. You can unplug the power from the back of your power supply or from the wall outlet.

4. Locate the correct button on your motherboard. If you’re not sure where to find it, look at your motherboard’s manual.

cmos-reset-motherboard-button

5. Press and hold the button for five to ten seconds with your finger or the eraser end of a pencil. If you use your finger, make sure to ground yourself by tapping a bare metal surface (doorknobs are great) before touching anything inside your computer.

6. Reconnect your computer to power and reboot.

7. Press the correct key to enter your BIOS options. Most motherboards use the “Delete” key, but look for your splash screen.

8. Adjust your BIOS options as necessary.

If you have no other way to reset your CMOS, you can erase saved settings by removing the CMOS battery. This battery allows the volatile CMOS memory to stay powered even when the computer is disconnected from an outlet. By removing and replacing the battery, you’ll erase the CMOS, forcing a reset.

1. Turn off your computer.

2. Press the power button multiple times to clear any capacitors.

3. Disconnect your computer from the wall outlet.

4. Find the CMOS battery on your motherboard. This is most commonly a CR2032 battery, a coin-sized battery seen below. You’ll find it near the PCI Express slots on most motherboards. Consult your motherboard’s manual for its exact location.

reset-cmos-battery-1

5. Gently remove the CMOS battery. If it is secured by a metal clip, slide the battery out from under the clip. Take care not to bend the clip.

6. Wait a few minutes, then replace the CMOS battery.

7. Reboot your computer.

By manually adjusting the right jumper, you can trigger the CMOS clearing function.

1. Turn off your computer.

2. Press the power button multiple times to clear any capacitors.

3. Disconnect your computer from the wall outlet.

4. Open your computer case and locate the CMOS clearing pins. It will typically be a two- or three-pin configuration mounted on the motherboard labelled “CLEAR,” “RESET” or even “CLRPWD” for “clear password.”

cmos-reset-jumper-reset-bios

5. On a three-pin configuration with a shared middle pin, move the plastic jumper over to connect the middle pin and the previously disconnected pin. For a two-pin configuration, remove the jumper completely.

6. Wait a few minutes, then return the jumper to its original configuration.

7. Reboot your computer.

You will be able to reset your CMOS using any of the above methods. Let us know if it is working for you.

Image credit: Toniperis (Own work)

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