CMOS
lastmod 2020-06-28created 2016-05-143 edits
CMOS (Complementary metal–oxide–semiconductor, pronounced "see-moss") is a type of integrated circuit used to build digital circuits such as microprocessors and SRAM. The term complementary metal-oxide semiconductor (相補性 金屬 酸化膜 半導體) is also in common use.
In the world of small-scale computers such as personal computers and workstations, the non-volatile memory used to store and keep the current time and hardware information (called the BIOS) is sometimes called CMOS ROM, or simply CMOS, and the stored data itself is also sometimes called CMOS. For example, the expression "reset the CMOS when the motherboard doesn't work" is used.
About
The CMOS setup of a typical computer is the procedure in which the user saves to the BIOS/UEFI which hard disks are installed in the computer, which VGA card is used, and so on, telling the computer which peripherals are installed and how to control them. This is where things get caught, and overclocking, hardware issues, and the boot order are also set here. Touching it wrongly can cause serious problems for the computer. There have even been reported cases of burning out a CPU by messing this up.
Because it is powered by a separate battery so that its contents are kept even when the computer is turned off, it starts losing its memory once the battery dies. If the CMOS keeps getting erased, replace the battery. The exact location differs by motherboard, and the manual shows where it is. In this case it shows symptoms such as the system time being reset to January 1, 1970 or to the motherboard's year of manufacture. Of course, some products are fine even if you remove and reinsert the battery. People often call it a mercury battery, but mercury batteries have not been used for a long time, and it is actually a lithium battery. It was used to lower the price of the CMOS battery. The reason it is called CMOS is also that it traditionally stored the BIOS settings by supplying battery power to CMOS SRAM, hence the name CMOS.