FEX Runs on ReactOS ARM64, x64 Games Work

Efforts to run x86_64 software on the experimental ARM64 build of ReactOS, the open-source Windows-compatible OS, have moved forward. A developer has combined it with FEX to achieve a setup capable of launching x64 Windows games on ARM hardware. According to reporting by Michael Larabel of Phoronix, the effort, while still experimental, marks a significant milestone. Released footage shows Super Mario 64 running.

he’s paired that “open-source Windows” OS with the open-source FEX emulator for in turn being able to run Windows x64 games/apps on ReactOS atop native ARM hardware

As the quoted passage indicates, the base is ReactOS running on ARM64, with an instruction-translation layer stacked on top in a dual-layer structure. The previous milestone in x86 compatibility is covered in detail in ReactOS Achieves Half-Life 2 Compatibility: 30 Years of the Open-Source Windows-Compatible OS. This latest achievement can be positioned as extending that compatibility layer to a different instruction set architecture. Target devices include the Raspberry Pi 5 and Raspberry Pi 3, bringing it closer to an environment that can be tested at hand.

Current Status and History of ReactOS on ARM64

ReactOS is a publicly developed OS that aims for binary compatibility with Windows drivers and applications. Development has long focused on x86, with ARM64 support proceeding as an experimental branch. According to reporting by Michael Larabel of Phoronix, booting on real ARM64 hardware only began to come together earlier this year. The work has been led by Ahmed Arif, known as SidiHmeed. He has been continuously working on the ARM64 port and peripheral support. Even now, the ARM64 version remains experimental and is not polished enough for daily use. Still, it has progressed step by step from booting to basic operation to peripheral recognition. The recent FEX integration is an attempt to broaden compatibility along that same trajectory.

The difficulties in ARM support lie in differences in the kernel, boot process, and device descriptions. Raspberry Pi models differ in peripheral configurations, requiring individual adjustments. Unless display, storage, and I/O initialization are stable, the upper compatibility layer cannot be tested. Developers have accumulated boot tests on real hardware, gradually increasing the number of supported models. This maturation of the foundation became a prerequisite for FEX integration. The focus is shifting from merely booting to running applications. While it remains experimental, the scope of testing has clearly widened.

How x64 Compatibility Works via FEX Integration

FEX is an instruction-translation platform for running x86 and x64 software on ARM64. It has a track record of use in Linux environments and continues to be improved through open development. At its core, it translates x86 instructions into ARM64 instructions while bridging system calls. Because ReactOS provides a Windows-compatible system-call interface, interfacing with the translation layer is the key issue. In this work, FEX runs on ReactOS ARM64, and on top of that, x64 Windows binaries are launched. The OS itself runs natively on ARM64, with only applications executed via translation. The distinctive feature is the stacking of two compatibility technologies.

Instruction translation adds overhead, so performance is lower than native execution. In time-sensitive areas such as graphics and audio processing, delays and glitches are likely. Still, older titles and office applications with modest requirements may fall within a practical range. FEX reduces overhead for repeatedly executed code through dynamic recompilation and caching mechanisms. The more accurate ReactOS’s system-call implementation is, the less burden falls on the translation layer. The maturity of each affects the other. This demonstration shows that the interface works at a basic level. Expanding coverage will require close examination of individual calls and exception handling.

Demonstrated Operation and Expanded Device Support

In the released footage, Super Mario 64 launched and ran with on-screen graphics. The video was posted on X and shared by the ReactOS project as a milestone. In his Phoronix report, Michael Larabel emphasizes that an x64 Windows entertainment application ran on ARM64 hardware. It is significant as an example involving graphics rendering, not just a boot check. Because entertainment applications handle graphics, audio, and input simultaneously, they serve as material for validating multiple functions at once. Although confirmed with only a limited title, it corroborates the effectiveness of the stacked configuration. Future testing will focus on reproducibility with other applications.

On the hardware side, booting was reported on the Raspberry Pi 3 in addition to the Raspberry Pi 5. For the Raspberry Pi 3, custom Ethernet and Wi-Fi drivers were prepared. Progress in testing even on older-generation single-board computers shows a widening target base. Because boot procedures and peripheral support differ between old and new models, the development burden is heavy. Still, an environment testable on readily available hardware will lead to more participants. As more real-hardware test reports come in, isolating bugs will become faster. Development speed depends on the spread of supported hardware and the volume of test reports. This expansion works to strengthen that cycle.

Remaining Challenges and Outlook for

Commercial Use

The current setup is for research, development, and testing, and is not at the stage for production use. ReactOS ARM64 itself is an experimental build, with stability and device support still incomplete. FEX integration has also not yet reached extensive compatibility testing beyond basic operation checks. Required system calls and external components differ by application, requiring case-by-case support. Quantitative information, such as performance measurements and long-run records, is also lacking. For commercial or business use, reproducibility and established maintenance procedures are essential. At present, trial use by developers and testing contributors remains central.

Security and operational readiness also remain challenges. While a Windows-compatible OS can run existing software, it may also inherit legacy vulnerabilities. Without systems for distributing updates and fixing defects, operational risks increase. When considering use on ARM devices, the quality of peripheral drivers is also important. Custom drivers broaden testing, but a long-term maintenance outlook is needed. Improved documentation and installation procedures would reduce the burden on testers. As an open development project, progress depends on contributions and test reports. Building on this achievement, further work is needed on both compatibility coverage and stability.

Editorial Opinion

Over the next three to six months, we expect experimental use of ReactOS ARM64 to spread among developers. We expect sharing of FEX integration procedures and bug information to advance, and the range of working applications to become clearer. We expect reproduction reports on readily available hardware such as the Raspberry Pi 5 to increase, accelerating the development cycle.

Over a one- to three-year period, the combination of a Windows-compatible OS and instruction translation could become established as one option. Evaluation is likely to advance for uses that both preserve x86 assets and take advantage of the power efficiency of ARM hardware. We assess that stability and maintenance structures will be prerequisites for enterprise adoption.

The remaining question is where to draw the line on performance overhead and compatibility. What level of operation should be considered practical, and the criteria are now at issue. With limited development resources, what should be set as the priority?

References

• “ReactOS Dev Gets FEX Running For x86_64 Games On This “Open-Source Windows” OS Under ARM”, by Michael Larabel — Phoronix, 2026-09-09T20:15:11.000Z (ARR)
• Source URL: https://www.phoronix.com/news/ReactOS-FEX-ARM64-Stacking