How to Clear Your Computer's CMOS Memory

What clearing CMOS actually does

Clearing CMOS resets your computer's BIOS settings back to the factory defaults. This means your motherboard forgets any custom settings you or a technician changed — boot order, fan speeds, overclocking adjustments, security passwords — and returns to the state it shipped in. The CMOS is a small battery-backed memory chip that holds these settings even when your computer is powered off.

Most people clear CMOS when they've changed a setting that now prevents the computer from starting, when they've forgotten a BIOS password, or when they're troubleshooting a hardware problem and need to rule out BIOS configuration as the cause. It does not erase your hard drive, your operating system, or any of your files — those live on a different part of your computer.

Key Takeaways

Clearing CMOS resets BIOS settings to factory defaults but does not touch your files, operating system, or hard drive.
The three main methods are removing the CMOS battery, using the CMOS jumper on the motherboard, or using a BIOS menu option if your computer still starts.
You will need to open your computer case and locate the CMOS battery or jumper, which requires a Phillips screwdriver and about 10 to 15 minutes.
After clearing CMOS, you may need to reconfigure settings like boot order, date and time, or security features before the computer works normally again.

Method 1: Remove the CMOS battery

This is the most straightforward method and works on almost every desktop computer. Shut down your computer completely, unplug the power cable from the wall, and wait 30 seconds. Open the case — usually by removing the side panel with a Phillips screwdriver. Locate the CMOS battery on the motherboard; it looks like a large coin cell (similar to a watch battery) sitting in a small round socket.

Press the clip or edge of the socket gently to pop the battery out. Leave it out for at least 10 to 15 minutes — this drains the residual charge that keeps the CMOS memory alive. Reinsert the battery, close the case, plug in the power cable, and start the computer. The CMOS is now cleared.

Method 2: Use the CMOS jumper

Many motherboards have a three-pin jumper labeled CLR_CMOS, CLEAR CMOS, or similar. This is a small plastic connector that you move to change which pins are connected. Shut down and unplug the computer, then open the case and locate the jumper on the motherboard — the manual or a label on the board itself will tell you where.

The jumper normally connects two of the three pins. Move it to connect the other two pins (usually the middle and third pin) for about 10 seconds, then move it back to its original position. Close the case, plug in the power cable, and start the computer. This method is faster than removing the battery and carries less risk of dropping a small component.

Method 3: Clear CMOS from the BIOS menu

If your computer still starts and you can enter the BIOS setup, you may be able to reset settings without opening the case. Restart the computer and press the key to enter BIOS — usually Delete, F2, F10, or F12, depending on the manufacturer. The correct key usually appears on the screen during startup.

Once in the BIOS menu, look for an option like "Reset to Defaults", "Load Defaults", "Restore Defaults", or "Factory Reset". Select it and confirm. The BIOS will reset to factory settings, and you can then exit and restart the computer. This method only works if the computer starts and you can reach the BIOS menu — if a BIOS password is blocking you or the computer won't start at all, you'll need to use the battery or jumper method instead.

What to do after clearing CMOS

After the CMOS is cleared, your computer may behave differently on the first startup. The date and time will reset to a default (often 2000 or 2020), and the boot order may change. If you had disabled certain hardware or set custom fan speeds, those changes are gone. The computer should start normally, but you may see warnings about the date being wrong or about hardware changes.

If you cleared CMOS to fix a startup problem, the computer should now start. If it does not, the problem is likely not BIOS-related. If you cleared CMOS to remove a BIOS password, you can now enter the BIOS menu again without a password. You will need to reconfigure any settings you want to change from the defaults — boot order, security features, or hardware settings — before the computer is back to your preferred configuration.

When clearing CMOS won't help

Clearing CMOS only affects BIOS settings. It will not fix problems caused by failed hardware, corrupted operating system files, malware, or driver issues. If your computer won't start because of a bad hard drive, a failed power supply, or a memory module that has gone bad, clearing CMOS will not solve it. If your computer starts but Windows won't load, or if you're seeing error messages from your operating system, the problem is not in the BIOS.

Clearing CMOS also will not recover a lost BIOS password if the password is stored on a separate chip rather than in the CMOS battery-backed memory — some newer systems use this approach. If you're locked out of the BIOS and clearing CMOS doesn't work, you may need to contact the computer manufacturer or a technician.

Safety precautions while opening your computer

Before you open the case, shut down the computer completely and unplug the power cable from the wall. Do not just put it to sleep or shut it down while plugged in — residual power can cause damage if you touch the wrong components. Wait at least 30 seconds after unplugging to let capacitors discharge.

Ground yourself before touching the motherboard by touching a metal part of the case or wearing an anti-static wrist strap. This prevents static electricity from damaging sensitive components. Avoid touching the CPU, RAM, or other chips directly. Take a photo of the motherboard before you start, so you can remember where everything was if you need to put it back. Work slowly and do not force anything — if a component does not come out easily, you may be pulling the wrong way.

Frequently Asked Questions

Will clearing CMOS delete my files or operating system?

No. CMOS only stores BIOS settings, not files or operating system data. Your hard drive and everything on it remain unchanged. Clearing CMOS is safe for your data.

How long does it take to clear CMOS?

Using the battery method takes about 10 to 15 minutes total, including opening the case and reinserting the battery. Using the jumper method is slightly faster. Using the BIOS menu method takes only a few minutes if the computer starts.

What if I clear CMOS and the computer still won't start?

The problem is likely not BIOS-related. Check that the power cable is plugged in, that the monitor is connected and powered on, and that RAM is fully seated in its slot. If the computer still does not start, the issue may be a failed power supply, bad memory, or a failed hard drive — clearing CMOS cannot fix those.

Do I need to reinstall Windows after clearing CMOS?

No. Windows and all your programs remain on the hard drive and will load normally. You may see a message about the date being wrong on first startup, but Windows will function as before. You only need to reconfigure BIOS settings if you had changed them from the defaults.

Can I clear CMOS on a laptop?

Most laptops do not have a removable CMOS battery or jumper. Some newer laptops have a BIOS reset option in the BIOS menu itself. Check your laptop's manual or contact the manufacturer. If your laptop has a BIOS password you cannot bypass, you may need to send it to the manufacturer for a reset.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.