Valve Uses FEX and Wine for SteamOS Game Compatibility

Valve is expanding its efforts to ensure a wide range of games are playable on its Linux-based SteamOS, particularly for devices like the Steam Deck. While the Proton compatibility layer has become well-known for enabling Windows games to run on SteamOS, Valve is now integrating two additional, less-discussed compatibility layers: FEX and Wine. These layers are crucial for broadening the library of games accessible to SteamOS users.

The first of these new layers is FEX, which is Valve's implementation of fex-emu. FEX is an open-source project designed to emulate x86 processor instructions on Arm chipsets. This technology has evolved significantly since its inception in 2018, growing from a small cross-platform emulation project into a sophisticated system. According to its website, fex-emu now features an advanced binary recompiler capable of supporting all modern extensions of the x86(-64) instruction set. To enhance performance and reduce overhead, the emulator can interface directly with graphics libraries such as OpenGL and Vulkan. Steam's internal developer documentation indicates that FEX also utilizes code caching to minimize stuttering, aiming for a smoother gaming experience.

Valve's involvement with FEX predates its integration into SteamOS. Valve engineer Pierre-Loup Griffais mentioned last year that the company has been providing financial support to Ryan Houdek, the lead developer of FEX, even when the project was in its early prototype stages. At that time, Valve projected that it would require nearly a decade of development before FEX-emu would be sufficiently robust for widespread reliance. This long-term investment highlights Valve's commitment to overcoming architectural barriers for game compatibility.

While Proton itself is built upon the pre-existing Wine conversion tool, the introduction of FEX signifies a new dimension in Valve's compatibility strategy. Wine, which stands for "Wine Is Not an Emulator," is a compatibility layer that translates Windows API calls into POSIX calls on-the-fly, allowing many Windows applications to run on Unix-like operating systems such as Linux. By combining the established capabilities of Wine with the specialized x86-on-Arm emulation provided by FEX, Valve aims to create a more comprehensive and performant gaming environment on SteamOS. This multi-layered approach addresses different technical challenges, ensuring that a broader spectrum of Windows games can be successfully adapted for Valve's own operating system and hardware.