Clearing the CMOS resets your BIOS settings to factory defaults, which solves some hardware problems but erases any custom configurations you've made

Your CMOS is a small chip on your motherboard that stores BIOS settings — things like boot order, fan speed, and overclocking adjustments. When you clear it, you're telling that chip to forget everything and start over with the manufacturer's original settings. This is useful when your computer won't start, won't recognize a hard drive, or is stuck in a boot loop. It's not useful if you've spent time tuning performance settings or if you're trying to fix a software problem.

The process itself is straightforward: you either remove a coin-sized battery from the motherboard for a few minutes, flip a jumper switch, or use a BIOS menu option — depending on your motherboard model. After the reset, your computer will boot normally, but you'll need to reconfigure anything you'd customized, including the date and time.

Key Takeaways

  • Clearing CMOS resets BIOS settings to factory defaults and can fix boot failures, unrecognized hardware, or systems stuck in restart loops.
  • The reset erases custom settings like overclocking, boot order changes, and security passwords, so you'll need to reconfigure them afterward.
  • Three methods exist: removing the CMOS battery for 10–30 seconds, moving a jumper switch, or using a BIOS menu option — which one depends on your motherboard.
  • Clearing CMOS does not fix software problems, malware, or corrupted operating systems; it only resets hardware-level configuration.

When clearing CMOS actually solves the problem

Clearing CMOS works best when your computer has a hardware configuration issue that's preventing it from starting. If your system won't boot at all, shows a black screen with error codes, or keeps restarting before the operating system loads, a CMOS reset can often get you back to a working state. The most common scenario is when you've changed a BIOS setting — like disabling a built-in device or changing memory timings — and the system no longer boots as a result.

It also helps when your motherboard doesn't recognize a newly installed hard drive, SSD, or RAM. Sometimes a BIOS setting is configured in a way that blocks detection of new hardware. Resetting to defaults often allows the motherboard to auto-detect components correctly. If you've forgotten a BIOS password you set yourself, clearing CMOS will remove it, though this doesn't work for passwords set by your computer's manufacturer or administrator.

What you'll lose when you clear CMOS

Any setting you've customized in the BIOS will revert to the manufacturer's default. This includes boot order (which device your computer tries to start from first), fan curves, RAM timing adjustments, overclocking settings, and any security features you've enabled like Secure Boot or TPM. If you've tuned your system for performance or stability, you'll need to redo that work after the reset.

Your system date and time will also reset to a default value, usually sometime in the past. This can cause problems with Windows activation, SSL certificate validation, and file timestamps until you correct it. Any BIOS passwords you created will be erased — but again, this only applies to passwords you set yourself, not ones set by your computer's manufacturer or IT department.

The three ways to clear CMOS

Removing the battery is the most common method. Shut down your computer completely, unplug the power cable, and wait at least 30 seconds. Open the case and locate the CMOS battery — it's a small, round, silver coin-cell battery, usually labeled CR2032. Gently pry it out with a plastic tool or your fingernail, wait 10–30 seconds, then reinstall it. Close the case, plug in the power, and start the computer.

Using the jumper switch is faster if your motherboard has one. Locate the three-pin jumper labeled CMOS, CLR_CMOS, or similar on your motherboard manual. Move the jumper from pins 1–2 to pins 2–3 for about 10 seconds, then move it back. This shorts the CMOS circuit and clears the settings without removing the battery. Not all motherboards have this option.

Using the BIOS menu is available on newer motherboards. If your computer still boots into BIOS (usually by pressing Delete, F2, or F12 during startup), look for an option called "Reset to Defaults", "Load Optimized Defaults", or "Clear CMOS" in the main menu. Select it, confirm, and reboot. This is the safest method because you don't have to open the case.

What clearing CMOS does not fix

Clearing CMOS will not solve software problems, malware infections, corrupted Windows installations, or driver issues. If your computer boots into Windows but runs slowly, crashes, or shows error messages, the problem is in your operating system or software, not your BIOS. A CMOS reset won't help. Similarly, if your computer is infected with malware, clearing CMOS won't remove it — the malware lives in your hard drive or SSD, not in the CMOS chip.

It also won't fix hardware failures like a dead hard drive, failing RAM, or a broken power supply. If your motherboard itself is damaged, a CMOS reset won't bring it back to life. The reset only changes configuration settings; it doesn't repair or replace broken components.

What to do after you clear CMOS

After the reset, your computer should boot normally. The first thing to do is correct the date and time — go to your system settings and set it to the current date. Then check that your hard drives and other devices are still recognized in BIOS. If you had customized any settings before the reset, you'll need to reconfigure them now.

If your computer still won't boot after clearing CMOS, the problem is likely hardware failure or a corrupted operating system, not a BIOS configuration issue. At that point, you may need to reinstall Windows, run hardware diagnostics, or consult a technician. If the reset did fix your boot problem, take note of what setting caused the issue so you can avoid it in the future.

Frequently Asked Questions

Will clearing CMOS delete my files or operating system?

No. CMOS only stores BIOS settings, not files or Windows. Your documents, programs, and operating system remain on your hard drive. The reset only changes hardware configuration, not what's stored on your storage devices.

Can I clear CMOS while the computer is powered on?

No. You must shut down completely and unplug the power cable before removing the battery or moving the jumper. Working on the motherboard while powered can damage components or injure you. Wait at least 30 seconds after unplugging before opening the case.

What if I don't know which jumper is the CMOS jumper?

Check your motherboard manual — it will show the exact location and label. If you don't have the manual, search the motherboard model number online and download the PDF. If you're uncomfortable locating it, removing the battery is a safer alternative that works on all motherboards.

Will clearing CMOS remove my Windows password?

No. Your Windows login password is stored on your hard drive, not in CMOS. Clearing CMOS only removes BIOS passwords you set yourself. Your Windows account remains protected.

How often should I clear CMOS?

Only when you have a specific problem — a boot failure, unrecognized hardware, or a BIOS setting that's preventing your system from working. There's no reason to clear it otherwise. It's a troubleshooting step, not a maintenance task.