The Apollo guidance computer had firmware consisting of a specially manufactured core memory plane, called "core rope memory", where data were stored by physically threading wires through (1) or around (0) the core storing each data bit.Originally, it meant the contents of a writable control store (a small specialized high speed memory), containing microcode that defined and implemented the computer's instruction set, and that could be reloaded to specialize or modify the instructions that the central processing unit (CPU) could execute.Most computer peripherals are themselves special-purpose computers.Devices such as printers, scanners, cameras and USB flash drives have internally stored firmware; some devices may also permit field upgrading of their firmware.Since 1996, most automobiles have employed an on-board computer and various sensors to detect mechanical problems.As of 2010, modern vehicles also employ computer-controlled anti-lock braking systems (ABS) and computer-operated transmission control units (TCUs).Firmware can either provide a standardized operating environment for the device's more complex software (allowing more hardware-independence), or, for less complex devices, act as the device's complete operating system, performing all control, monitoring and data manipulation functions.Typical examples of devices containing firmware are embedded systems, consumer appliances, computers, computer peripherals, and others.
Over time, popular usage extended the word "firmware" to denote any computer program that is tightly linked to hardware, including processor machine instructions for BIOS, bootstrap loaders, or the control systems for simple electronic devices such as a microwave oven, remote control, or computer peripheral.
Firmware such as the program of an embedded system may be the only program that will run on the system and provide all of its functions.
Before the inclusion of integrated circuits, other firmware devices included a discrete semiconductor diode matrix.
As originally used, firmware contrasted with hardware (the CPU itself) and software (normal instructions executing on a CPU).
It was not composed of CPU machine instructions, but of lower-level microcode involved in the implementation of machine instructions.