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In electronic systems and computing, firmware is the combination of persistent memory and program code and data stored in it. Typical examples of devices containing firmware are embedded systems (such as traffic lights, consumer appliances, and digital watches), computers, computer peripherals, mobile phones, and digital cameras. The firmware contained in these devices provides the control program for the device. Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory. Changing the firmware of a device may rarely or never be done during its economic lifetime; some firmware memory devices are permanently installed and cannot be changed after manufacture. Common reasons for updating firmware include fixing bugs or adding features to the device. This may require physically changing ROM integrated circuits, or reprogramming flash memory with a special procedure. Firmware such as the ROM BIOS of a personal computer may contain only elementary basic functions of a device and may only provide services to higher-level software. 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 integrated circuits, other firmware devices included a discrete semiconductor diode matrix. The Apollo guidance computer had firmware consisting of a specially manufactured core memory plane, called "core rope memory", where data was stored by physically threading wires through (1) or around (0) the core storing each data bit.
Flashing (or flashing firmware) refers to the overwriting of existing firmware or data on ROM modules present in an electronic device with new data. This can be done to upgrade a device  or to change the provider of a service associated with the function of the device, such as changing from one mobile phone service provider to another or installing a new operating system.
Ascher Opler coined the term "firmware" in a 1967 Datamation article. 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. 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. It existed on the boundary between hardware and software; thus the name "firmware".
Until the mid-1990s, updating firmware typically involved replacing a storage medium containing firmware, usually a socketed ROM. Flash memory allows firmware to be updated without physically removing an integrated circuit from the system. An error during the upgrade process may make the device non-functional, or "bricked".
In some respects, the various firmware components are as important as the operating system in a working computer. However, unlike most modern operating systems, firmware rarely has a well-evolved automatic mechanism of updating itself to fix any functionality issues detected after shipping the unit.
The BIOS may be "manually" updated by a user, using a small utility program. In contrast, firmware in storage devices (harddisks, DVD drives, flash storage) rarely gets updated, even when flash (rather than ROM) storage is used for the firmware; there are no standardized mechanisms for detecting or updating firmware versions.
Most computer peripherals are themselves special-purpose computers. Devices such as printers, scanners, cameras, USB drives, have firmware stored internally. Some devices may permit field replacement of firmware.
Some low-cost peripherals no longer contain non-volatile memory for firmware, and instead rely on the host system to transfer the device control program from a disk file or CD.
As of 2010[update] most portable music players support firmware upgrades. Some companies use firmware updates to add new playable file formats (encodings); iriver added the Vorbis format this way, for instance. Other features that may change with firmware updates include the GUI or even the battery life. Most mobile phones have a Firmware Over The Air firmware upgrade capability for much the same reasons; some may even be upgraded to enhance reception or sound quality, illustrating the fact that firmware is used at more than one level in complex products (in a CPU-like microcontroller versus in a digital signal processor, in this particular case).
Since 1996 most automobiles have employed an on-board computer and various sensors to detect mechanical problems. As of 2010[update] modern vehicles also employ computer-controlled ABS systems and computer-operated Transmission Control Units (TCU). The driver can also get in-dash information while driving in this manner, such as real-time fuel-economy and tire-pressure readings. Local dealers can update most vehicle firmware.
Examples of firmware include:
Sometimes third parties create an unofficial new or modified ("aftermarket") version of firmware to provide new features or to unlock hidden functionality. Examples include:
These hacks usually take advantage of the firmware update facility on many devices to install or run themselves. Some, however, must resort to exploits in order to run, because the manufacturer has attempted to lock the hardware to stop it from running unlicensed code.