CMOS is a type of integrated circuit technology used in personal computers to store basic information needed by the BIOS to start the computer. It controls various functions, including POST, and settings such as hard drives, boot preferences, and overclocking. Changes can be made in the setup screen accessible during boot by pressing a key, and modifications should be made by experienced users. Most motherboard manuals provide a complete list of available CMOS options.
A complementary metal oxide semiconductor (CMOS) is a type of integrated circuit technology. The term is often used to refer to a battery-powered chip found in many personal computers that contains some basic information, including the date and time and system configuration settings, needed by the Basic Input/Output System (BIOS). ) to start the computer. This name is somewhat misleading, however, as most modern computers no longer use these chips for this function, but instead depend on other forms of non-volatile memory. CMOS chips are still found in many other electronic devices, including digital cameras.
In a computer, the chip controls a variety of functions, including the Power On Self Test (POST). When the computer’s power supply turns on, CMOS runs a series of checks to make sure that the system is functioning properly. One of these checks includes counting random access memory (RAM). This delays the boot time, so some people disable this feature in their CMOS settings, opting for a fast boot. If installing new RAM it is best to enable the feature until the RAM has been checked.
After POST is complete, CMOS does other settings. Hard drives and formats are detected, along with redundant array of independent disks (RAID) configurations, boot preferences, presence of peripherals, and overclocking changes. Many settings can be changed manually within the CMOS setup screen to improve performance; however, modifications should be made by experienced users. Changing settings incorrectly can make your system unstable, cause crashes, or even prevent your computer from starting up.
The setup screen is accessible during boot POST by pressing a key before the operating system initializes. Normally this is the Delete key, but it could be another. A line of text will indicate which key will take the user to the CMOS or BIOS setup screen. Changes cannot be made within an operating system such as Microsoft Windows®, but must be made within a true DOS session. There is also an option to protect settings by requiring a password to change settings. The changes are saved when you exit by pressing the F10 key, then the computer restarts to use the new settings.
Most motherboard manuals provide a complete list of available CMOS options. These vary by motherboard design and BIOS manufacturer.
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