What is CMOS?
CMOS is a special kind of memory maintained by a small battery after you turn the computer off. The BIOS uses CMOS to store the settings you select in Setup and to maintain the internal real time clock (RTC). Every time you turn on your computer, the BIOS uses the CMOS settings to configure your computer. If the battery charge runs too low, the CMOS contents will be lost and POST will issue a “CMOS invalid” or “CMOS checksum invalid” message. If this happens, you may have to replace the battery. Contact your manufacturer for assistance. After the battery is replaced, the proper settings will need to be restored in Setup.
Complementary metal oxide semiconductor (CMOS) is a type of semi-conductor chip that holds data without requiring an external power source. In a personal computer (PC), CMOS holds the basic instructions the computer needs to initialize its hardware components and boot up. These settings are known as the basic input output settings (BIOS), also referred to as CMOS settings. CMOS controls a variety of functions, including the Power On Self Test (POST). When the computer’s power supply fires up, CMOS runs a series of checks to make sure the system is functioning properly. One of these checks includes counting up random access memory (RAM). This delays boot time, so some people disable this feature in the CMOS settings, opting for a quick boot. If installing new RAM it is better to enable the feature until the RAM has been checked. Once POST has completed, CMOS runs through its other settings. Hard disks and formats are detected, along with Redundant Array of Independent Disk (RAID) config
Complementary metal-oxide semiconductor, or CMOS, typically refers to a battery-powered memory chip in your computer that stores startup information. Your computer’s basic input/output system (BIOS) uses this information when starting your computer. CMOS-related error messages could be caused by a faulty or discharged battery. The battery can become discharged if your computer has been turned off for a very long time. To resolve CMOS-related errors, check the information that came with your computer or contact your computer manufacturer. Because your CMOS settings are specific to your computer’s hardware, Microsoft cannot provide specific instructions for changing them.
CMOS, short for Complementary Metal Oxide Semiconductor, is a low-power, low-heat semiconductor technology used in contemporary microchips, especially useful for battery-powered devices. The specific technology is explained in detail on this CMOS definition page. Most commonly, though, the term CMOS is used to refer to small battery-powered configuration chips on system boards of personal computers, where the BIOS stores the date, the time, and system configuration details.
