It existed on the boundary between hardware and software; thus the name "firmware".
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.
Almost all electronic devices beyond the simplest contain some firmware.
Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory.
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.
Some companies use firmware updates to add new playable file formats (codecs); iriver added Vorbis playback support this way, for instance.
It was not composed of CPU machine instructions, but of lower-level microcode involved in the implementation of machine instructions.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.most portable music players support firmware upgrades.If firmware is upgradable, it is often done via a program from the provider, and will often allow the old firmware to be saved before upgrading so it can be reverted to if the process fails, or if the newer version performs worse.Sometimes, third parties create an unofficial new or modified ("aftermarket") version of firmware in order to provide new features or to unlock hidden functionality; this is referred to as custom firmware.As of 2010, modern vehicles also employ computer-controlled anti-lock braking systems (ABS) and computer-operated transmission control units (TCUs).