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What Is CMOS?


A CMOS battery backup for BIOS on a motherboard.
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If you’re having boot or show points in your laptop, you might be more likely to come throughout suggestions about clearing the CMOS. However what does CMOS do, and the way is it associated to BIOS? Right here’s the whole lot you’ll want to know.

BIOS Configuration Storage

The time period CMOS, pronounced as “sea-moss,” is usually used to explain a small reminiscence on a pc motherboard that shops BIOS or UEFI settings, together with system date, time, and {hardware} configuration.

CMOS is brief for Complementary Metallic-Oxide-Semiconductor, which is a kind of fabrication course of used within the building of assorted built-in circuit (IC) chips, together with the reminiscence chip getting used to retailer the BIOS settings.

Additionally it is known as CMOS RAM, BIOS RAM, and non-volatile BIOS reminiscence. Whereas CMOS is mostly related to Home windows computer systems, Macs have the same reminiscence, and it’s known as NVRAM or PRAM.

How Are BIOS and CMOS Associated?

A computer chip on a motherboard
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To know the relation between BIOS and CMOS, it helps to know the function of a BIOS in your laptop. BIOS, quick for Primary Enter-Output System, is a firmware that comes together with your laptop’s motherboard. It’s liable for initializing your laptop’s {hardware}, testing it, and booting up the working system whenever you hit the facility button.

Nevertheless, as BIOS is saved in read-only reminiscence, it may possibly’t save any modifications you make to its configuration, akin to tweaks to the boot order or overclock settings. These modifications, together with the system date and time, are saved in CMOS. So CMOS might be important to your laptop’s secure functioning. And in case your CMOS is cleared or its battery fails, you lose all of your BIOS tweaks, and it reverts to the default settings.

What Is a CMOS Battery?

Person installing a lithium CR2025 battery as a backup on a motherboard.
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The CMOS battery is often a CR2032 lithium coin battery in your laptop’s motherboard. It was historically used to energy the CMOS as older motherboards used a unstable reminiscence to retailer the BIOS settings. Unstable reminiscence loses knowledge when it loses energy. So a battery was used to supply energy to the reminiscence even after you had shut down the pc or eliminated the facility wire.

Nevertheless, the fashionable UEFI motherboards use a non-volatile reminiscence or NVRAM to retailer UEFI configuration knowledge. The non-volatile reminiscence can retain knowledge even with out utilized energy. That stated, CMOS batteries are nonetheless used to maintain time in your laptop. And for the reason that removing or failure of CMOS battery has historically been related to clearing CMOS knowledge, trendy motherboards additionally reset UEFI settings when CMOS battery fails.

Most CMOS batteries final wherever between two to 10 years, relying on the pc utilization. But when your laptop is displaying the improper system time or date after a reboot or you might be dealing with {hardware} compatibility points, it could be time to interchange the CMOS battery. Different key signs of a failed CMOS battery embody issues within the boot course of and fixed beeping noise from the motherboard. You might also get errors, akin to “CMOS Learn Error,” “CMOS Battery Failure,” and “CMOS Checksum Error.”

The way to Clear CMOS

There are events when you might have to clear your laptop’s CMOS to reset BIOS or UEFI settings. Nevertheless, it’s a comparatively simple course of, and relying on whether or not or not you could have entry to BIOS or UEFI menu, there are a couple of methods to attain this.

One of many best methods to clear CMOS is by going to the BIOS or UEFI settings and selecting the reset possibility. It’s usually known as “Load manufacturing facility defaults” or “Load setup defaults.” You may as well use the CMOS clear button if obtainable in your motherboard. This button can both be discovered on the IO plate or close to the CMOS battery.

Clear CMOS button.
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As well as, reseating the CMOS battery is one other method to clear the CMOS knowledge. However you have to to open your laptop and entry the motherboard to reseat or change the battery. However don’t fear. You will discover detailed directions and extra methods to clear your laptop CMOS in our detailed information.

Small however Essential Half

CMOS is a nifty little part that almost all laptop customers by no means have to fret about. Additionally, there is no such thing as a profit in tinkering with it until you might be troubleshooting your laptop and must revert BIOS or UEFI to its default settings. So you possibly can neglect about CMOS till you want it.





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