BIOS (an acronym for Basic Input/Output System) is
|“||[t]he set of routines stored in read-only memory on a system circuit board that starts a computer, then transfers control to the operating system. The BIOS opens communication channels with computer components such as the hard disk drives, keyboard, monitor, printer, and communication ports.||”|
Modern computers such as desktop and laptop computers contain program code that facilitates the hardware initialization process. The code is stored in non-volatile memory and is commonly referred to as boot firmware. The primary firmware used to initialize the system is called the "Basic Input/Output System" (BIOS) or the "system BIOS".
The system BIOS is the first piece of software executed on the main central processing unit (CPU) when a computer is powered on. While the system BIOS was originally responsible for providing operating systems access to hardware, its primary role on modern machines is to initialize and test hardware components and load the operating system. In addition, the BIOS loads and initializes important system management functions, such as power and thermal management. The system BIOS may also load CPU microcode patches during the boot process.
System BIOS is typically developed by both original equipment manufacturers (OEMs) and independent BIOS vendors, and is distributed to end users with computer hardware. Manufacturers frequently update system firmware to fix bugs, patch vulnerabilities, and support new hardware. The system BIOS is typically stored on electrically erasable programmable read-only memory (EEPROM) or other forms of flash memory, and is modifiable by end users. Typically, system BIOS firmware is updated using a utility or tool that has special knowledge of the non-volatile storage components in which the BIOS is stored.
- NIST Special Publication 800-147, at 1-3.