FCode

FCode is a Forth-like programming language used as the firmware scripting language for Open Firmware, an open, platform-neutral interface specified by IEEE 1275. It is designed to run inside the firmware environment to perform hardware initialization, device enumeration, and bootstrap tasks across a range of architectures. FCode source is typically compiled into Open Firmware bytecode that runs on a built-in interpreter within the firmware.

As a device- and platform-defining language, FCode provides primitive operations for interacting with the device tree, memory, I/O, and other firmware services. Its stack-based, postfix syntax is characteristic of Forth, but FCode includes domain-specific words and conventions that facilitate hardware discovery, property handling, and boot-time configuration. The language emphasizes portability of firmware components, enabling same Open Firmware code to run on different hardware platforms with appropriate drivers and device nodes.

Historically, FCode played a central role in Open Firmware implementations on Sun SPARC workstations and Apple Power Macintosh computers in the 1990s and early 2000s. It served both as a means to implement low-level firmware routines and as a vehicle for distributing platform-specific drivers and boot logic in a hardware-agnostic format. Over time, many Open Firmware environments migrated toward higher-level code and alternative boot frameworks, reducing the emphasis on FCode.

Today, FCode remains associated with legacy Open Firmware systems and open-source Open Firmware variants. While not widely used in contemporary consumer hardware, it is documented as part of the Open Firmware ecosystem and is encountered in historical discussions of firmware design and device initialization processes. See also IEEE 1275, Open Firmware, Forth.