( BIOS) - Software which provides basic low-level control of devices required to operate the system, such as the keyboard, floppy disk, and screen. On most systems the BIOS is stored in read-only memory inside the PC.

a built-in program on a computer that tracks and stores information about various computer components so that the operating system can function properly.

A small section of code which is loaded from a separate ROM chip during boot-up. The BIOS defines how the OS interacts with hardware, as well as configuring devices and loading the OS. All low level functions are defined in the BIOS instructions, allowing for a more generic hardware. Also, by having all low level functions defined by the BIOS information, updates to low level operations can be made without replacing the hardware. BIOS are hardly ever changed, but can be flashed with new instructions if they need to be updated.