Though often interchangeably used, the two terms refer to different things. BIOS (Basic Input Output System) refers to a set of instructions that are critical for the functioning of the system. These instructions include information about the components connected to the motherboard, like the hard disk, RAM, and the configuration of the many onboard subsystems. CMOS (Complementary Metal Oxide Semiconductor) refers to the chip on which the BIOS instructions are stored. CMOS is the name of the technology behind the chip that stores the BIOS. Present-day CMOS is technically called EEPROM for Electronically Erasable Programmable Read-only Memory. These can be rewritten to, and this allows the BIOS instructions of a motherboard to be updated when required. The process of updating the BIOS instructions is called Flashing.