what is cmos
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CMOS definition & meaning

CMOS stands for “Metal-Oxide-Semiconductor”, which is used for constructing integrated circuit chips including microprocessors, microcontrollers, memory chips, and more. But today, CMOS has different meanings in different areas. CMOS refers to a sensor type in the photography field. But for computers, it is commonly used for the chip stores the BIOS information. In this entry, we will inform you about the CMOS for computers.

CMOS is a chip that stores BIOS configuration data, such as CPU voltages, RAM latencies, integrated peripheral states, hard disk boot priorities, and more, located on the motherboards. CMOS also handles the clock for the computer. It uses a volatile, low-power complementary metal-oxide-semiconductor SRAM, as we mentioned in the first paragraph.

CMOS is volatile, which means when it loses power, it loses all of its data. It relies on a CMOS battery to keep its data even if the power was cut off. This design also serves as a safety measure. When a user changes a setting that may cause the computer to not boot at all, the user can just unplug the PC as well as the CMOS battery to apply a factory reset to whole BIOS settings. Some motherboards also have jumpers or buttons to cut the battery power from the CMOS chip.

In the modern motherboards, BIOS has been replaced with its more advanced version, UEFI. Both BIOS and UEFI must be kept in non-volatile memory because if their data is lost, the computer will not work. The configuration data is kept in an NVRAM, non-volatile RAM, alongside the UEFI itself. However, even if the configuration is kept in non-volatile memory, it still deletes itself for the aforementioned safety measure when the power is cut.

Why do we use CMOS?

We use CMOS to keep the BIOS settings in it. All of the configurations that we change in the BIOS are kept in the CMOS chip.

Where is the CMOS battery located?

The CMOS battery is located on the motherboard. It is generally kept close to the middle of the board. However, it may also be slightly to right-bottom or can be completely covered with cooling/styling components of the motherboard.

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