BIOS is variously referred to as "Basic Input Output System" or "Binary Input Output System". BIOS is what gets the computer up and running at startup. BIOS is intended to provide the basic input/output services between the computer's mainboard and its busses, disks, card slots and controller chipsets. Newer BIOS is often built with a SYMBIOS link to the Desktop Management Interface in the operating system allowing the operating system to directly query and change BIOS settings (such as date and time) while running. The term BIOS should be used to refer to the actual ROM or Flash ROM or EPROM containing the program code gets the computer running and helps it load an operating system. The BIOS frequently stores values it determines what type of hardware is installed or after configuration changes are made through its configuration interface. The memory where these BIOS settings are stored is called the CMOS. The two terms are frequently (and mistakenly) used to refer to the BIOS itself.
When powered on, the BIOS is copied from the ROM into RAM and begins to run. The BIOS performs a POST (Power On Self Test) of the computer hardware, establishes communication with a boot device, searches for the operating system on that device, loads the operating system from disk. Today's modern BIOS is stored in EPROMS.