Firmware has evolved to mean the programmable content of a hardware device, which can consist of machine language for a microprocessor, or configuration settings for a fixed-function device or programmable logic device. Many, though not all, devices have firmware that can be updated after manufacturing. This is usually done electronically in modern systems, however sometimes the storage medium containing the firmware, such as a socketed ROM, must be replaced.
Firmware may expose an externally accessible interface. For example, in some modem implementations the firmware is not directly accessible, but is part of a combination of hardware and firmware that responds to commands from the host system.
Firmware has traditionally been stored in ROM; however cost and performance requirements have driven component vendors to adopt various replacements, including non-volatile media such as EEPROM and Flash, or SRAM solutions, such as the firmware loaded by an operating system device driver, as described below.
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