CMOS stands for Complementary Metal-Oxide-Semiconductor and is a small area of memory on your motherboard that is used to store your BIOS settings. This allows your BIOS settings to be stored directly on your motherboard so you can access them at any time, even without additional memory or an operating system on your PC.
Resetting the CMOS probably isn't your first port of call when you're having problems with your PC, but it's an important step in the troubleshooting process and is generally simple enough that everyone should know how to do it. Whether you're experiencing system freezes at startup, problems after changing BIOS settings, or something just doesn't feel right after installing a new RAM kit, resetting your CMOS can sometimes be the easiest solution.
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First things first
Let us not act hastily
Before we get into resetting the CMOS, there are a few things we can try. The first thing you should do, depending on the issue at hand, is to make sure everything is installed correctly. If you're having display issues, check that your RAM, GPU, and monitor are all connected properly. If your PC is randomly turning off, check that your power supply is properly connected to the main power outlet and to the motherboard. You may also want to check your CPU temperatures, as your PC may automatically shut down if they get too high.
If you've just installed new hardware on your PC and everything was fine before, it might be worth checking for BIOS and driver updates. While many things are plug-and-play these days, sometimes they still need a little updating to make sure they work as intended.
Before resetting the CMOS, always turn off the power (if applicable) and unplug the power cord directly from the device.
Using the motherboard reset buttons
I/O and main header area on the back
The easiest way to reset the CMOS is if your motherboard has CMOS reset buttons. Unfortunately, not all motherboards have these, but it's becoming more common to see them recently. These buttons can be found in two places. The first is on the rear I/O, where you connect all your peripherals, monitors, etc. The second is somewhere on the motherboard itself, usually either near the 24-pin power connector or further down by all the jumpers and headers.
Resetting the CMOS using these buttons is quite simple. As mentioned above, unplug your power supply and then hold down the CMOS reset button for 5-10 seconds. Then everything should be fine. When you turn on your PC after that, it will usually display a message saying that some settings have been changed and ask you to enter the BIOS to check everything. When you see this, you know it worked correctly.
Removing the CMOS battery
Yup, take it out right away
Almost as easy as pressing the reset button, but not quite. Almost all motherboards have a small battery. Usually it's a flat CR2032, but not always. Once you find it, you'll notice there's a small metal tab on one side. Pushing in on that metal tab will release the battery and remove power from the motherboard.
There is always speculation about how long it takes to remove the battery. In all my years of working on PCs, I have found that 30-60 seconds is more than enough. If your motherboard still has a power button connected, you can press that for 10-15 seconds as well to make sure all power is drained from the motherboard. Again, make sure the power supply is unplugged from the wall outlet before doing this.
Using the jumper pins on the motherboard
Old method, but still worth knowing
One of the original and probably most annoying ways to clear your CMOS is to jumper a pair of pins on the motherboard. The reason for this is because these pins can be found almost everywhere on the motherboard and sometimes aren't always clearly labeled. Once you find them, it gets a little easier.
To reset the CMOS this way, you'll need to “jump” the pins or connect them somehow. Many older motherboards came with a small plastic jumper tool for this purpose, but you can also use anything metallic to connect the pins, such as a pin, screwdriver, or even a butter knife. You'll need to be careful not to scratch the motherboard, and as always, make sure the power supply is unplugged from the mains socket.
Why do I need to reset my CMOS?
The main reason to reset your CMOS is when something isn't working properly. It sounds silly, but doing so can make troubleshooting problems with your PC a lot easier, and in some cases, fix the problem at hand. Here are some examples of things that might cause you to want to reset your CMOS.
- Virus: There are some nasty viruses that can sometimes change your PC settings and cause major problems. Depending on the problem, resetting your CMOS may be the solution if you were unable to solve your problems by using antivirus software.
- Overclocking failed: If you've recently tried overclocking your CPU or RAM and things just don't seem right, resetting the CMOS may help. This will reset all of the BIOS settings for your CPU and RAM to default and you should be able to start over again.
- Black screen when booting: This can be caused by a faulty overclock or many other things. Double check that your RAM is installed correctly and that your GPU and monitor are also connected correctly. If everything looks fine, you may need to reset the CMOS to get back to the BIOS default settings.
- Random Blue Screen of Death: This can often be caused by faulty RAM, but that is not always the case. Sometimes resetting the CMOS can help fix problems in the BIOS settings and avoid a Blue Screen of Death (BSOD).
- Installing new hardware: In most cases, it is not necessary to reset the CMOS before installing new hardware. However, if you upgrade your CPU and/or RAM and have changed some BIOS settings, it may be easiest to simply reset the CMOS to restore the default settings.
Sometimes there is no rhyme or reason as to why computers start giving you problems. However, having the right knowledge to fix those problems when they arise is a whole different story. Most people use a computer almost every day, either at home or at work. Being able to do a little troubleshooting before calling an IT professional can help you resolve problems as quickly as possible.