What Is CMOS?


A CMOS battery backup for BIOS on a motherboard.

In case you are having boot or show points in your pc, you’re prone 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 could know.

BIOS Configuration Storage

The time period CMOS, pronounced as “sea-moss,” is often 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 development of varied built-in circuit (IC) chips, together with the reminiscence chip getting used to retailer the BIOS settings.

It is usually known as CMOS RAM, BIOS RAM, and non-volatile BIOS reminiscence. Whereas CMOS is mostly related to Home windows computer systems, Macs have an analogous reminiscence, and it’s referred to as NVRAM or PRAM.

How Are BIOS and CMOS Associated?

A computer chip on a motherboard

To grasp the relation between BIOS and CMOS, it helps to know the position of a BIOS in your pc. BIOS, brief for Primary Enter-Output System, is a firmware that comes along with your pc’s motherboard. It’s answerable for initializing your pc’s {hardware}, testing it, and booting up the working system whenever you hit the facility button.

Nonetheless, as BIOS is saved in read-only reminiscence, it could’t save any modifications you make to its configuration, corresponding to tweaks to the boot order or overclock settings. These modifications, together with the system date and time, are saved in CMOS. So CMOS will be important to your pc’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.

The CMOS battery is often a CR2032 lithium coin battery in your pc’s motherboard. It was historically used to energy the CMOS as older motherboards used a risky reminiscence to retailer the BIOS settings. Unstable reminiscence loses information 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 twine.

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

Most CMOS batteries final anyplace between two to 10 years, relying on the pc utilization. But when your pc is displaying the fallacious system time or date after a reboot or you’re dealing with {hardware} compatibility points, it could be time to exchange the CMOS battery. Different key signs of a failed CMOS battery embrace issues within the boot course of and fixed beeping noise from the motherboard. You may additionally get errors, corresponding to “CMOS Learn Error,” “CMOS Battery Failure,” and “CMOS Checksum Error.”

Find out how to Clear CMOS

There are events when you’ll have to clear your pc’s CMOS to reset BIOS or UEFI settings. Nonetheless, it’s a comparatively easy course of, and relying on whether or not or not you’ve entry to BIOS or UEFI menu, there are just a few methods to realize this.

One of many best methods to clear CMOS is by going to the BIOS or UEFI settings and selecting the reset choice. It’s sometimes referred to as “Load manufacturing unit 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.

As well as, reseating the CMOS battery is one other solution to clear the CMOS information. However you will want to open your pc and entry the motherboard to reseat or substitute the battery. However don’t fear. You could find detailed directions and extra methods to clear your pc CMOS in our detailed information.

Small however Essential Half

CMOS is a nifty little element that the majority pc customers by no means have to fret about. Additionally, there is no such thing as a profit in tinkering with it except you’re troubleshooting your pc and must revert BIOS or UEFI to its default settings. So you’ll be able to overlook about CMOS till you want it.

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