ReactOS is an independently developed open-source operating system. ReactOS is not a Linux-based system and doesn't shares any of the UNIX architecture. ReactOS has an interface that mimics the older Windows operating systems.


  • ReactOS is able to run Windows software
  • ReactOS is able to run Windows drivers
  • ReactOS looks-like Windows
  • ReactOS is free and open source

What is ReactOS?

ReactOS is a free and open source operating system written from scratch. Its design is based on Windows in the same way Linux is based on Unix, however ReactOS is not Linux. ReactOS looks and feels like Windows, is able to your run Windows software and your Windows drivers, and is familiar to Windows users.

Is ReactOS free?

Free and Open Source. Free as "you can download it for free", and open source..which means…you can see how ReactOS is coded, you can modify it, you can provide patches for any bugs you find, and even more: You can create your own ReactOS versions! You're using Open Source software daily if you use Firefox, LibreOffice, OpenOffice, GNU-Linux distributions among zillions of Open Source projects out there. The Open Source projects, as ReactOS, are driven for and by its Community, so being active translating, donating, or coding is a way to help ReactOS boost forward.

What are the differences between Windows and ReactOS?

There are mainly two. Firstly ReactOS is open source. Secondly ReactOS is Free. Also Windows (especially the newer versions) are known to monitor all your activity by default. So if you're concerned about your privacy or just don't want to share any personal info, we promise (and you can check our source code) that we don't track any of your data.

Can I install ReactOS and run any software compatible with Windows on it?

Probably yes. However we highly recommend to check first if your favourite app runs in ReactOS. ReactOS is still an on-going project and not all the apps and drivers runs perfect on it. The best way to check the compatibility is to install ReactOS inside a virtual machine (a step by step and video guide can be found here) and try your own needs. There are tons of pieces of software and, as you may imagine, is impossible to track all of them.

What's New

Hello ReactOS followers and enthusiasts! It has been quite a long time since we published the 101th newsletter and so far no further updates have been posted since then. While the ReactOS Twitter account does provide announcements, posts about working applications and such from time to time, much of what is happening with the project as a whole isn't mentioned. Most of what we are going to talk about is the current situation with releases and overall ReactOS development.

Why does it take so long to release a new version of ReactOS? Are you guys dead?

The latest release of ReactOS is 0.4.14, published on 16th December, 2021. That release alone took a year to be engineered. Back then, ReactOS followed a 3-month cadence, releasing a new version every 3 months. But since 2021, ReactOS is still at 0.4.14. Are you guys dead?

The answer is certainly no, the way we handle releases has changed. Back in the day, ReactOS releases were made for the sake of quantity rather than quality. Every new release after 3 months was similar to the previous one, with the exception of a small number of added features and bug fixes. But overall, the net gap between the releases wasn't that big. For a while now we have instated a rule that for a new version to reach "Release" status, it needs to have a reasonably low amount of regressions (no more than 20) and the stability mustn't be badly impacted by the introduction of new features or code changes done during development.

In other words, the ReactOS project is now focusing on providing quality releases, which rules out the 3-month release cadence. That previous approach wasn't feasible for a development team with a size like ours anyway.

It is expected that it will take longer for a new release to be published, although these releases will now be much more substantial, with a much bigger number of improvements. If you're impatient to test the latest changes and features you can always try the nightly builds (also called experimental builds).

Development status

In the last year and during the beginning of 2023, the ReactOS developers and contributors alike are working on many parts of the project, the top focused area being the kernel. Other areas that aren't kernel-related are the applications, specifically our Paint and Notepad programs, the Input Method Editor (IME) as well as other stuff such as the ReactOS testing infrastructure.

ReactOS x64 port status

The x64 port of ReactOS, while still in its infancy, has steadily gotten better in terms of stability. Back then ReactOS could barely boot and if it ever did, it usually resulted in an immediate crash or a BSoD by just doing simple tasks. With the help of Timo Kreuzer (tkreuzer), the x64 port has gotten to a somewhat tolerable state where ReactOS can now operate without big problems.

Although issues still do remain, and compatibility is inferior to the x86 version, more applications and even hardware drivers have started to work. Note that the x64 port currently will not run ANY x86 applications due to lack of WoW64.

WHS test fixes

The WHS test bot (acronym that stands for Windows Home Server) is a bot that runs Windows Server 2003 where it executes the whole ReactOS testsuite infrastructure, ensuring that each testcase passes the test results on a Windows environment. This helps understanding how Windows behaves when certain test inputs are being given to it. WHS testcase infrastructure was known to fail a lot due to tests not passing, or even crashing. On January of 2023 during the hackfest, Timo Kreuzer (tkreuzer), Mark Jansen (learn_more) and Thomas Faber (ThFabba) worked together to fix some of the testcases. Thanks to their efforts, WHS can now pass all the tests.

Paint & Notepad improvements

Thanks to Katayama Hirofumi MZ both Paint and Notepad have received quality of life improvements, miscellaneous fixes and whatnot. Notably, he fixed some flickering issues on Paint when resizing the application's window and implemented the "text tool" feature. In addition, he improved the performance of Notepad, implemented the "Now Printing" dialog and provided some miscellaneous fixes.

Security Subsystem improvements

George BiÈoc (GeoB99) has progressively improved the Security Subsystem (Se) of the kernel with new stuff as well as bug fixes, mostly notably improving the security access checks and access tokens.

An access check is an action done by the kernel to verify that if an object can be accessed by a requestor. If the requestor does not have the right privileges to access an object or the object itself prevents others from doing certain actions imposed by an access control list (ACL), access is denied. There was a hack in SepAccessCheck where access was granted to anybody, regardless of the security restrictions imposed by security descriptors. This could lead to bad actors tamper and toy around with objects.

Thanks to his work, the hack in SepAccessCheck has been removed and security access checks are now operational and the kernel can prevent any unauthorized access from whoever tries to access an object with improper access rights. His future plan for the Security Subsystem is to implement security auditing of all objects and miscellaneous improvements where needed.

Registry improvements

For ReactOS to reach Beta phase it has to solve two major milestones – stability and corruptions. Usually corruptions in ReactOS can manifest in form of filesystem and registry corruptions. While filesystem corruptions can be prevented by choosing a more modern filesystem such as BtrFS which is what we currently support, registry corruptions are by themselves a death sentence as ReactOS currently doesn't implement any self-healing mechanisms to recover the system from corrupted registry hives. As a result, the user is forced to do a clean reinstallation of the system. Worst case, the system would still boot up but be stuck on the login prompt dialog (aka the "Ctrl+Alt+Del" dialog) as the user profile has been corrupted or missing. The latter generally happens after ReactOS is forcefully shutdown after a clean install.

George BiÈoc is currently working on improving the registry by implementing the necessary registry self-healing mechanisms and CmCheckRegistry, a fundamental function that validates the registry for any corrupted parts of the registry and takes appropriate actions at recovering a registry hive from such corrupt parts. While his work is currently in progress (#4571), so far he has received some positive results from testers. A small piece of his work has been merged, which fixes the registry flusher of ReactOS not working for almost a decade! This fix also solves the problem of the missing user profile due to forcefully shutting down the system, and as such you should no longer expect to see the infamous "Ctrl+Alt+Del" dialog prompt as often as before.

In addition he is working on the registry cache implementation (#5088), as ReactOS doesn't properly sync the cached information which leads to inconsistent results.

Currently most of this work is still being upheld because it makes our bootloader size larger than it should be, preventing the AMD64 build of ReactOS booting up.

IME project

The Input Method Editor (or IME) is a component that facilitates the typing of characters not originally present on the input devices by using a sequence of characters. IME in ReactOS has been for the most part a stub, but thankfully Katayama Hirofumi MZ has extensively worked on it. This greatly helps with CJK support, as well as allowing installation of custom IMEs for different locales. Katayama wrote an article about his work, the Japanese part of it was written using MZ-IME in ReactOS, here is the English part of it:

Seven months have passed since my last report, and I would like to explain the current status of Japanese input in ReactOS. We have confirmed that Japanese ReactOS recognizes and can actually use MZ-IME Japanese input, a home-made test IME.

After the IMM32 implementation was almost complete, the remaining issue was the implementation on the USER32 side, where the default procedure and the processing of the default IME window and EDIT control had not yet been written. The default procedure required the handling of several IME messages. The default IME window is an invisible window that is essential in IME messaging; the EDIT control is a so-called text box that required proper handling of some IME messages. When IME message handling was implemented, the IME composition string window and candidate window were displayed correctly.

Note that Japanese input for Command Prompt and Rich Edit Control is not yet available. Several glitches and instabilities remain. Please note that the ReactOS IMM is currently developed for older systems and does not support the newer TSF-compatible IMEs. Defects and problems can be reported at

Other highlights

  • Dmitry Borisov (disean) fixed a BSoD that was caused due to a shutdown with the IDE driver stack from Windows Server 2003.
  • The Win32 backend kernel-mode subsystem component (win32k.sys) is steadily being improved with improvements and bug fixes by many people, notably Timo Kreuzer, James Tabor (jimtabor), Jerome Gardou (zefklop), Thamatip Chitpong (TAN-Gaming) and Katayama Hirofumi MZ.
  • Some parts of the Session Manager SubSystem (SMSS) have been cleaned up and revamped by Hermès Bélusca-Maïto (#4821). This includes cleaning up old and deprecated code in the SM client library (SMLIB). Furthermore, one API has been implemented in order to allow ReactOS to use other subsystems other than the Win32 one. In addition, the Client/Server Runtime Subsystem (CSRSS) has been slightly adapted for this purpose (#4802).