ReactOS and WDDM support: status, challenges, and progress

ReactOS has been in development for so long that many of the current contributors weren't even born when it began, but its goal remains unchanged: deliver an ABI experience compatible with Windows capable of running software and drivers designed for the Microsoft system. In recent years, one of the most ambitious fronts of the project has been to catch up with support for hardware.

That process has led to a key goal: getting closer to the modern Windows graphics driver architecture. We're talking about WDDM, the model that replaced XDDM since the Vista era. Within the ReactOS ecosystem, Exploring WDDM means understanding how GPU management has changed, which parts of the system were restructured and why it is not enough to simply “activate” a driver to make everything work like in Windows.

What is WDDM and why it makes a difference

Related article:

Everything ReactOS Can't Do Against Windows: A Complete, Updated Analysis

WDDM, the Windows Display Driver Model, introduced a profound overhaul of the graphics stack: moved control of the GPU from components like Win32k to a dedicated core (Dxgkrnl.sys) that communicates with the manufacturer's miniports. Each revision (1.0, 1.1, 1.2, and later) defines which interfaces the system offers and how they are implemented, a concept distinct from the Direct3D feature levels seen in DxDiag.

This more modular and demanding architecture goes beyond what XDDM offered. In WDDM, Dxgkrnl acts as orchestrator, and the vendor driver facilitates clear entry points and contracts. This separation allows for improvements such as virtualized video memory, a GPU scheduler, and, in general, greater stability by moving some of the logic to user mode.

For years, practical documentation for in-depth video driver development was scarce for either architecture, which hampered progress. With the maturity of open GPU drivers, the community has gained real references to understand how OpenGL ICDs behave, Vulkan support, and model transitions.

What happened to XDDM? Compatibility, leftovers, and the breaking point

Since Windows 8, the system requires the GPU driver to be WDDM; however, XDDM didn't disappear completelyWindows Vista and 7 allowed XDDM drivers to be loaded without complaint, and there are still legacy mechanisms that coexist with WDDM. The module that loads OpenGL ICDs, for example, barely changed between versions.

Communication in WDDM to the miniport is more direct. Win32k retains a syscall jump that Dxgkrnl fills with the appropriate interface, reducing the involvement of the old subsystem in GPU logic. In fact, when the system boots, specific routines are observed to link WDDM to the old Win32k world without interfacing architectures.

There are two display drivers that you should know in detail: TSDDD.dll and CDD.dll. The first, TSDDD, It is loaded manually in session 0 and it's a very basic XDDM driver that barely writes to blank memory. In the NT5.x family (as the basis for ReactOS), a failed video initialization often results in a bugcheck for video failure; in Vista and later, this "real" situation no longer occurs thanks to the second component.

CDD.dll is the interesting one. While acting as an XDDM driver, it issues IOCTLs to talk to WDDM. It's the only way Dxgkrnl and Win32k communicate meaningfully during modern graphical operation. During initialization, Win32k queries for adapters, but the response is overwritten by cdd.dll, ensuring the bridge to WDDM. A critical point: once WDDM is enabled, it is not possible to run an XDDM driver in parallel.

OpenGL ICD, Vulkan and the relationship with the system

OpenGL ICDs are loaded using the traditional module, and its flow does not vary excessively between Vista, 7, 8, and later, which facilitated cross-testing using ICDs from different generations. Vulkan behaves similarly: the system delegates interaction with the GPU to these layers, but in WDDM, the miniport and Dxgkrnl establish the actual hardware “contract.”

This hybrid structure explains why we still see remnants of XDDM coexisting with WDDM in system components. The CDD.dll bridge allows Win32k to continue fulfilling its classic role without blocking the modern path, while Dxgkrnl and miniport take over the critical task of managing the GPU.

Compiling WDDM drivers for testing on ReactOS

To start a WDDM driver you need an auxiliary piece: displib.lib of the WDK, which exposes the entry point to initialize the driver and “wake up” Dxgkrnl without binding against it. The flow is particular: the initialization API is invoked, data structures are passed to Dxgkrnl, and then Dxgkrnl returns control by calling the callback of Boot from the provider's miniport.

That callback provides the interfaces for the rest of the communication with Dxgkrnl. At this point, Win32k doesn't look anything at the start of the miniport, which is a fundamental difference from the XDDM world. This adaptation was straightforward to implement in ReactOS, opening the door to importing and compiling WDDM drivers that also continue to work on Windows.

WDDM in ReactOS: Screen-first focus

The D3DKMT APIs are used for DirectX and OpenGL acceleration, so for the first experiment on ReactOS we opted for Focus on the basics: getting video outputThis is where the VidPn (Video Presentation Network) universe and the associated hardware support within Dxgkrnl come into play.

Since Windows 8 there are the so-called KMDOD, a variant of WDDM miniports that they dispense with 3D accelerationThey are easier to understand and get started with: they allow you to manage video modes, monitors, and trajectories without relying on the planner and other complex Dxgkrnl subsystems.

For ReactOS, the experiment was to build a minimal Dxgkrnl that would query the available modes via VidPn, hand them over to CDD, and activate CDD when Dxgkrnl was ready. The result: the system started talking to its first WDDM driver now show image in real conditions.

First successes: BasicDisplay.sys and vendor drivers

When loading BasicDisplay.sys into ReactOS, the conclusion was unexpectedly positive: WDDM turned out to be more tolerant than expected.It was even possible to launch vendor drivers solely for the display portion, without requiring them to support 3D acceleration.

In later tests, video outputs appeared with more drivers, including a driver for Nvidia from the era of Windows 7, which allowed ReactOS Move modern monitors to their native resolution and frequencyThe bottleneck wasn't Win32k, but actual hardware support, which is still being expanded.

Why XDDM is still crucial on the road to WDDM

Even though the ultimate goal is WDDM, ReactOS requires its XDDM stack to be in very good shape. The reason is that components such as CDD.dll and DWM itself They depend on the old world performing well to bridge the gap between the old and the new. In fact, DWM introduces demands that the current Win32k implementation in ReactOS can't yet fully meet, although there is continued progress.

Support for AMD GPUs under XDDM has also been accelerated, an important step to stabilize the field before opening the way to more complex WDDM driversThe chosen path is incremental: first screen and modes, then more puzzle pieces.

Key differences between XDDM and WDDM

One of the most notable changes in moving from XDDM to WDDM is fault handling. With WDDM, much of the driver logic is moved to user mode, which means that A driver crash doesn't have to bring down the system. complete. In addition, the GPU scheduler and virtualized memory allow for finer-grained resource allocation.

In XDDM, Win32k carried much more weight and communication with the hardware was more rigid. In WDDM, Dxgkrnl imposes a clear contract on miniports, and Win32k remains as a bridge to the windowing subsystem. This enables new capabilities such as DWM, compositing, and more reliable presentations.

• Planning and isolation of GPU work versus XDDM's monolithic approach.
• Virtual video memory and better management of shared resources.
• Increased stability when migrating driver logic to user mode.
• Integration with DWM and modern presentation routes.

Current limitations and work in progress

While WDDM display driver support in ReactOS is already a reality in testing, hardware compatibility continues to dictate the pace. Real devices require very specific supports, and each jump requires expanding subsystems: from plug and play to memory management and watchdogs.

At startup, communication is also observed between watchdog, Win32k and Dxgkrnl to prepare for the dispatch of the D3DKMT APIs within Dxgkrnl; this is a specific initialization step, but it adds additional requirements when it comes to faithfully reproducing Windows behavior.

Project status, community and call for collaboration

The recent push toward WDDM has been accompanied by more activity around hardware. There are technical articles detailing the process and Contributions are invited via donations, GitHub, or outreach.This is a large, long-distance front: each miniport and each presentation route adds nuances.

It is worth remembering, in passing, the nature of the project: ReactOS not Linux ni Unix. For a comparative analysis, is written from the ground up to be binary compatible with Windows, allowing it to run Windows software and drivers natively without resorting to compatibility layers like Wine/Proton, although the project also collaborates with that FOSS ecosystem to improve results.

Practical news: ReactOS 0.4.15 and system improvements

Beyond WDDM, version 0.4.15 has brought a good batch of changes: new drivers storage that improve stability and compatibility with units USB, as well as updated network drivers. Fonts, the desktop shell, Windows APIs, themes, and dialog boxes have also been tweaked.

Improvements have been made to caches and memory management that impact performance. In addition, Added support for LiveUSB Following deep modifications to the kernel's Plug and Play manager, opening the door to more third-party drivers, the graphical interface has received minor tweaks to make it easier to use compared to the text-based USETUP installer.

In the audio section, it is now possible to start with the Windows sound stack, although there are still rough edges to smooth out. It's also worth noting that 0.4.15 is the first release to support 64-bit architecture (amd64) up to the desktop, although there's no official 64-bit image yet because WOW64 is still being worked on.

Bug fixes have been intense: incorrectly assigned desktop icons Resolved issues include improved taskbar icons and native ZIP file support. All of this aims to improve the basic user experience while addressing hardware compatibility.

Download, installation and minimum requirements

ReactOS 0.4.15 images are available on SourceForge. It is possible test on virtual machine (recommended for starters) or install on real hardware with a USB drive created with utilities like Rufus, just like you would with standard Windows.

The requirements are modest: x86 CPU (Pentium or later), 64 MB of RAM, at least 450 MB of disk space on a FAT16/FAT32 partition and about 2 GB additional If you plan to install software or games, these minimums allow computers from the last decade or even older to run the system in testing scenarios.

Recommendations for use and realistic expectations

As of today, ReactOS is an experimental project. It is not recommended as a primary operating system if you need modern features and full compatibility with recent applications. For running newer software, Wine/Proton on Linux remains a very stable route with a large support ecosystem.

Still, the uniqueness of ReactOS makes it the The only open system that runs Windows binaries without any middleware emulator-style. This approach makes it interesting for laboratories, backward compatibility, analysis, and controlled environments where the behavior of applications and drivers needs to be studied.

Community context and common messages

In forums and social spaces, it is common to see reminders like: ReactOS is a PC system that can run Windows programs and drivers. Sometimes, member and online user counters are also displayed, simple indicators of community vitality that, without technical value, point to growing interest in the project.

Recent media narratives have even pointed out the temporal coincidence between the end of support for some versions of Windows and ReactOS's progress towards WDDMMore than an irony, it's a sign that the community is aligning priorities to remain relevant with current hardware and drivers.

In the end, all this effort converges on one point: build a solid foundation where WDDM can establish itself without abandoning the XDDM legacy that still acts as the glue between worlds. With CDD.dll as the bridge, Dxgkrnl as the brain, and miniports better understood thanks to open drivers, the path is paved, although there is still ground to cover.

Looking at all of the above, WDDM support in ReactOS is moving from a vague promise to a set of tangible milestones: Display drivers that start, modes that negotiate well, and monitors that work at full resolutionHardware compatibility needs to be scaled, pieces like WOW64 need to be completed, and Win32k and DWM need to continue to be fine-tuned, but the direction is clear and the community is already pushing in that direction.

Isaac

Passionate writer about the world of bytes and technology in general. I love sharing my knowledge through writing, and that's what I'll do on this blog, show you all the most interesting things about gadgets, software, hardware, tech trends, and more. My goal is to help you navigate the digital world in a simple and entertaining way.