In electronics and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices. Typical examples of devices containing firmware range from end-user products such as remote controls or calculators, through computer parts and devices like hard disks, keyboards, TFT screens or memory cards, all the way to scientific instrumentation and industrial robotics. Also more complex consumer devices, such as mobile phones, digital cameras, synthesizers, etc., contain firmware to enable the device's basic operation as well as implementing higher-level functions.
There are no strict boundaries between firmware and software, as both are quite loose descriptive terms. However, the term firmware was originally coined in order to contrast to higher level software which could be changed without replacing a hardware component, and firmware is typically involved with very basic low-level operations without which a device would be completely non-functional. Firmware is also a relative term, as most embedded devices contain firmware at more than one level. Subsystems such as CPUs, flash chips, communication controllers, LCD modules, and so on, have their own (usually fixed) program code and/or microcode, regarded as "part of the hardware" by the higher-level(s) firmware.
Low-level firmware typically resides in a PLA structure or in a ROM (or OTP/PROM), while higher level firmware (often on the border to software) typically employs flash memory to allow for updates, at least in modern devices. (Common reasons for updating firmware include fixing bugs or adding features to the device. Doing so usually involves loading a binary image file provided by the manufacturer into the device, according to a specific procedure; this is sometimes intended to be done by the end user.)
Thus, while high-level firmware (or software) typically is stored as a configuration of charges, low-level firmware may instead often be regarded as actual hardware in itself. For instance, older firmware was often implemented as a discrete semiconductor diode matrix. The modern equivalent is an integrated matrix of field effect transistors where 0's and 1's are represented by whether a particular component in the ROM and/or PLA matrices is present or not.
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