What Clearing Your CMOS Does to Your Computer

Clearing CMOS resets your BIOS settings to factory defaults, which solves boot problems but erases any custom configurations you made

When your computer won't start, gets stuck in a boot loop, or you've forgotten your BIOS password, clearing the CMOS (Complementary Metal-Oxide-Semiconductor) chip is one of the first things a technician will try. The CMOS chip is a small battery-backed memory module on your motherboard that stores your BIOS settings — things like boot order, fan speeds, overclocking adjustments, and security passwords. Clearing it wipes all those settings and returns them to what the manufacturer set them to originally.

This is different from updating your BIOS firmware. A BIOS update changes the actual code that runs on your motherboard. Clearing CMOS only resets the configuration data that code uses. You keep your current BIOS version; you just lose the choices you made within it.

Key Takeaways

Clearing CMOS erases all your BIOS settings and returns them to factory defaults, but does not affect your hard drive, files, or installed programs.
The most common reason to clear CMOS is to fix a computer that won't boot, especially if you recently changed BIOS settings or forgot a BIOS password.
You can clear CMOS by removing the battery from the motherboard for 10 to 30 seconds, or by using a jumper pin on the motherboard if your manual shows one.
After clearing CMOS, you will need to reconfigure settings like boot order, date and time, and any overclocking or fan adjustments you had made.

When clearing CMOS actually solves the problem

Clearing CMOS works best when the problem is something you changed in BIOS that broke the boot process. If you adjusted CPU voltage, memory timings, or boot order and now your computer won't start, resetting to factory defaults often gets you back to a working state. It also works if you enabled a security feature like a BIOS password and then forgot it — clearing CMOS removes the password entirely.

It does not fix hardware failures, driver problems, or corrupted Windows installations. If your hard drive is failing, your RAM is bad, or Windows won't load, clearing CMOS won't help. The same is true if your computer boots fine but runs slowly or crashes once it's in Windows — that's a software or driver problem, not a BIOS configuration problem.

A common scenario: you overclocked your CPU to squeeze out more performance, saved the settings, and now the computer won't boot. Clearing CMOS resets the CPU to its normal speed and usually solves it. Another: you changed the boot order to boot from a USB drive, removed the drive, and now the computer can't find anything to boot from. Clearing CMOS resets boot order to the default and the computer boots normally again.

How to clear CMOS on your motherboard

The method depends on your motherboard model, so check your motherboard manual first. Most modern boards use one of two methods: removing the CMOS battery or moving a jumper pin.

Battery method: Power off your computer completely and unplug it from the wall. Open the case and locate the CMOS battery — it looks like a large coin-cell battery (usually a CR2032) sitting flat on the motherboard. Note which way it faces, then gently pry it out with a plastic tool or your fingernail. Leave it out for 10 to 30 seconds, then press it back in the same way it was facing. Close the case, plug in the power, and turn the computer on. The BIOS will show default settings.

Jumper method: Some boards have a three-pin jumper labeled CLR_CMOS, CLEAR CMOS, or similar. Power off and unplug the computer. Locate the jumper on the motherboard and move the plastic cap from pins 1-2 to pins 2-3 for about 10 seconds, then move it back to 1-2. This shorts the CMOS and clears it. Close the case, plug in, and power on.

If your motherboard manual does not mention either method, or if you are uncomfortable opening the case, a technician can do this in a few minutes. It is not a complex procedure, but it does require you to identify the right component on your specific board.

What you lose when you clear CMOS

Any setting you changed in BIOS goes back to factory default. This includes boot order (which drive the computer tries to boot from first), date and time, fan speed curves, RAM timing adjustments, CPU voltage, and any overclocking settings. If you had enabled XMP or DOCP (automatic memory overclocking), that turns off. If you had set a custom fan curve so your computer runs quieter, it goes back to the manufacturer's curve.

You do not lose anything on your hard drive, SSD, or other storage. Your Windows installation, files, programs, and data are untouched. CMOS is separate from storage — it only holds BIOS configuration, not your actual data.

After clearing CMOS, you will need to go back into BIOS and reconfigure anything you had customized. If you had written down your settings before the problem happened, you can re-enter them. If not, you can usually leave everything at default and the computer will work fine — it will just run at standard performance rather than overclocked, and fans may run at their default speeds.

The difference between clearing CMOS and resetting Windows

Clearing CMOS is a motherboard-level reset. Resetting Windows (through Settings > System > Recovery) is an operating system reset. They are completely separate. Clearing CMOS does not touch Windows, and resetting Windows does not touch BIOS. If your computer boots into Windows but Windows is broken or slow, you need a Windows reset, not a CMOS clear. If your computer won't boot at all, a CMOS clear might help, but only if the problem is in BIOS settings.

A CMOS clear is also different from a BIOS update. Updating BIOS replaces the firmware code itself with a newer version. Clearing CMOS only resets the settings that code uses. You can clear CMOS without updating BIOS, and you can update BIOS without clearing CMOS.

When to try other things first

Before you open the case and clear CMOS, try these simpler steps: unplug the power cable for 30 seconds, then plug it back in and power on. This sometimes clears temporary BIOS glitches without opening the case. If the computer is stuck in a boot loop, try removing any USB drives, external hard drives, or SD cards, then power on again — sometimes the computer is trying to boot from a device that is no longer there.

If you recently installed new RAM or a new hard drive and the computer won't boot, reseat the RAM (remove it and push it back in firmly) or check that the hard drive cable is fully connected. These hardware connection issues are more common than BIOS problems and are worth checking first.

If the computer boots into Windows but is slow or crashes, the problem is almost certainly not BIOS. Run Windows Update, check for driver updates, run a malware scan, or check your hard drive health. Clearing CMOS will not fix any of these.

After you clear CMOS: what to do next

Once the computer boots successfully, go into BIOS (usually by pressing Delete, F2, or F12 during startup — your motherboard manual will say which) and check the settings. The date and time will be wrong, so set those first. Then check boot order to make sure your main hard drive or SSD is listed first. If you had any custom settings like XMP memory overclocking or fan curves, you can re-enable them now that you know the computer boots.

If the computer still won't boot after clearing CMOS, the problem is not a BIOS configuration issue. It could be a hardware failure, a corrupted Windows installation, or a bad hard drive. At that point, you would need to troubleshoot the hardware or reinstall Windows.

Frequently Asked Questions

Will clearing CMOS erase my files or programs?

No. CMOS only stores BIOS settings, not data. Your hard drive, files, Windows installation, and programs are completely separate and will not be affected. You will only lose the BIOS configuration choices you made.

What if I don't know my motherboard model?

You can find it by opening the case and looking at the motherboard itself — the model number is usually printed on the board. You can also use free software like CPU-Z or GPU-Z to identify it. Once you know the model, search for the manual online and look for CMOS clearing instructions.

Can I clear CMOS while the computer is powered on?

No. Always power off and unplug the computer before clearing CMOS. The battery keeps CMOS powered even when the computer is off, but you should still unplug to be safe and to avoid any electrical risk.

Do I need to clear CMOS before selling my computer?

It is a good idea if you had set a BIOS password, since clearing CMOS removes it. For privacy, it also resets any custom settings you made. However, it does not erase your hard drive — you should wipe your hard drive separately if you are concerned about data recovery.

What if clearing CMOS doesn't fix the boot problem?

Then the problem is likely hardware-related (bad RAM, failing hard drive, loose cables) or a corrupted Windows installation, not a BIOS setting. Try reseating RAM and hard drive cables, check that all power connections are find, or try booting from a Windows recovery USB to see if Windows can repair itself.

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.