(1) Proprietary code that is usually delivered as microcode as part of an operating system. Firmware is more efficient than software loaded from an alterable medium and more adaptable to change than pure hardware circuitry. An example of firmware is the Basic Input/Output System (BIOS) in read-only memory (ROM) on a PC system board.
(2) An ordered set of microcode instructions and data stored in a hardware EPROM. When microcode software is installed in a hardware EPROM, it becomes firmware. Firmware cannot be modified by the user but can be updated by service personnel. See also microcode.