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A microcontroller, like this PIC18F8720, is controlled by firmware stored inside in flash memory.

In computing, firmware is a computer program that is embedded in a hardware device, for example a microcontroller. It can also be provided on flash ROMs or as a binary image file that can be uploaded onto existing hardware by a user.

As its name suggests, firmware is somewhere between hardware and software. Like software, it is a computer program which is executed by a computer. But it is also an intimate and vital part of a piece of hardware, and has little meaning outside of that particular hardware.

The term "firmware" was originally used for micro-programs written for microsequencers such as AMD29xx. Later on, it was coined to indicate a functional replacement for hardware on low-cost microprocessors.

In practical terms, firmware updates can improve the performance and reliability, indeed even the basic available functionality of a device, and many devices benefit from regular firmware updates. One of the most common devices to have regular firmware updates are recording devices such as optical media writers (DVD, CD, HD DVD, Blu-ray), as media technologies extend, so firmware updates ensure hardware is kept up to date and compatible.

Firmware has evolved to mean the programmable content of a hardware device, which can consist of machine language instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device.

A common feature of firmware is that it can be updated post-manufacturing, either electronically, or by replacing a storage medium such as a socketed memory chip.

Firmware can — but is not required to — 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.

Most devices attached to modern systems are special-purpose computers in their own right, running their own software. Some of these devices store that software ("firmware") in a ROM within the device itself. Over the years, however, manufacturers have found that loading the firmware from the host system is both cheaper and more flexible. As a result, much current hardware is unable to function in any useful way until the host computer has fed it the requisite firmware. This firmware load is handled by the device driver.

Firmware in many devices can now be updated without the need for additional hardware, often through the use of vendor-provided software.

In some respects firmware is as much a software component of a working system as the operating system. However, unlike most modern operating systems, firmware rarely has a well evolved mechanism for updating itself to fix bugs and addressing functionality issues that are detected after the unit is shipped.

The easiest firmware to update is typically the system boot-related firmware, such as the BIOS in PCs. Some devices, such as video adapters and modems, frequently rely on firmware that is loaded dynamically by the operating system device driver, and thus is updated through the operating system update mechanisms entirely transparent to the user.

In contrast, storage device firmware is rarely updated with the same consistency as other parts of the system. Further, the mechanisms for detecting firmware versions and updating them are not standardized. As a result, these devices tend to have a significantly higher percentage of firmware-driven functionality issues, as compared to other parts of a modern computer system.

Examples of firmware include:

• The BIOS found in IBM-compatible Personal Computers;
• The platform code found on Itanium systems, Intel-based Mac OS X machines, and many Intel desktop boards is EFI compliant firmware;
• Open Firmware, used in computers from Sun Microsystems and Apple Computer;
• ARCS, used in computers from Silicon Graphics;
• RTAS (Run-Time Abstraction Services), used in computers from IBM;
• EPROM chips used in the Eventide H-3000 series of digital music processors.
• Adding features on the PSP
• The PS3 has updates similar to the PSP
• The iPod's control menus
• The Xbox 360 Dashboard Updates (like including 1080p HDTV Resolutions)
• The Common Firmware Environment (CFE)
• Timing and control systems for Washing machines
• FPGA and CPLD programming files used to configure hardware for a variety of purposes.
• Cisco IOS.
• The Wii's ability to download updates and new programs.

• ROM image
• BIOS
• LinuxBIOS
• Microcode

• Embedded Systems Glossary
• Firmware Definition Sharpened Glossary