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Revision as of 06:57, 9 March 2012 by BrentNewland (talk | contribs) (Why is the graphics subsystem not in Ring 3 but in Ring 0?=)
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See Also File Systems FAQ

See Also ReactOS Explorer & GUI FAQ

See Also ReactOS Website FAQ

See Also ReactOS Ports FAQ for questions about ARM, AMD64, and PowerPC


User FAQ

What is ReactOS?

ReactOS (short for React Operating System) is an open-source effort to develop a quality operating system that is compatible with Microsoft Windows applications and drivers.

Why re-implement NT?

First of all, the 'Windows' the general public knows is actually just one part of the modern Windows NT operating system. They usually mean the Win32 subsystem, a layer that sits upon the NT kernel, providing the user and application interface.

"NT is still around, known as XP and Vista"

Most people think of 'NT' as 'WinNT 4', while in reality the term NT refers to the NT series, which ranges from version 3 over NT5 (2000, XP, 2003) to NT6 (Vista, 2008 and 7).

The NT architecture was designed by a team lead by David Cutler, a former lead developer of VMS. It took them more than 4 years to combine the best of UNIX, VMS and OS/2 and create the NT architecture.

What about UNIX?

Mac OS X, Linux, BSD and other UNIX derivates share a common heritage based on a more than three decades old design of a simple basic operating system, that has evolved over time into a complex structure. Modern incarnations like Mac OS X put a fancy graphical user interface on top of UNIX, to hide system details, but focus mainly on beginners, and many advanced users are left out in the rain, as most advanced features cannot be accessed from the graphical user interface. Almost all UNIX flavors retain some of the original design flaws and binary compatibility between various versions is usually non-existent.

In theory there are a few UNIX standards like POSIX but in practice the standards are old and cover only the basic operating system and the terminal environment. Other standards such as the Linux Standard Base are often not implemented faithfully. As there is no user interface standard nor a standard API, most people still have to use command line applications or fight through the GUI mess. Many UNIX derivates use the de-facto standard X-Window system for graphical output, which might well possess one of the worst designs in software history. Still, modern UNIX derivates are trying to catch up with recent innovations and some of them already possess important features like access control list support.

In contrast to UNIX, ReactOS was designed for people familiar and comfortable with the Windows environment. Everything can be done through the well known Win32 user interface and advanced users are free to automate tasks with scripts or use the console.

Why use ReactOS?

A lot of people in popular discussion forums keep asking “why should I use ReactOS” or “why would someone need ReactOS” or “why not help develop Wine instead?” or “why not use Linux with Wine?”.

We have an answer for all these questions, but it's not some simple magic word. Let's name a few key issues here:

  • There are plenty of *nix operating systems out there, this is very good. However they have different targeting (they perfectly fit server market, but desktop still isn't conquered, and several factors work against most Windows alternatives out today).
  • There is currently no operating system which implements the kernel architecture design of MS Windows NT family (GNU/Linux is the best for comparison here: Linux was started as “clone” of Minix and Unix (eventually going on to be a Unix replacement), and ReactOS was started as “clone” of Windows NT).
  • Linux+Wine is never going to be a complete replacement for a full Windows system. It's not only because Linux (despite there are some really user-friendly Linux distros out there), and not only because many users might find a transition to Linux/BSD difficult, but it's due to design and implementation decisions of Linux and Wine architectures, which prevent 100% compatibility.
  • Even though Linux supports many types of hardware, Windows is still the dominant platform for device manufactorers. There are attempts to overcome this situation (like NDIS Wrapper for NT network card drivers, there are rumours about supporting NT video drivers, Captive NTFS for NT filesystem support), but ReactOS solves them from the first day by its design – be compatible with existing drivers and existing applications.
  • There are many people who do not like how *nix systems behave or dislikes the conventions used. For them, Linux, BSD, and Mac OS X are not options, even before application compatibility and hardware support come into play. An operating system should give the consumers what they want instead of demanding the consumer conform. Even with WINE, you are still running an operating system that behaves quite differently from Windows, at a user and system level.
  • Backwards compatibility. This is something vital for many people and companies, but the development philosophy of Linux and the GNU project do not consider it a priority. The Windows family has always went out of its way to ensure a stable API and backwards compatibility. By its design, ReactOS will also follow the philosophy of backwards compatibility with existing and future applications designed for the Windows NT family.

There are no plans for Windows to become released under a GPL-compatible license (at least, ReactOS team is not aware of them).

Finally, ReactOS offers a third alternative, for people who are fed up with Microsoft's policies but do not want to give up the familiar environment, architectural design, and millions of existing software applications and thousands of hardware drivers.

Is ReactOS based on Microsoft® Windows®?

No! ReactOS consists only of GNU GPL (General Public License) and GPL compatible licensed source code.

Is ReactOS based on *nix or Linux?

No! ReactOS is not based on UNIX/Linux. It's written from scratch.

Is ReactOS legal?

Yes. It's fully legal.

Developers have not looked at Windows® source code. They have used the public documentation of Windows® OSes. They have made several tests to understand how Windows® works. In fact, ReactOS does the same things Windows® does, but not exactly in the same way, because they haven't the same source code. All code in ReactOS is under the GNU GPL (General Public License).

Why does a certain application of mine not work under ReactOS?

ReactOS is in alpha stage and not recommended for everyday use. Many applications do not work (correctly) because many API calls simply haven't been implemented yet. This may be one of the reasons for the software not working.

Why ReactOS? Why clone Microsoft Windows?

First of all, ReactOS is not a clone of Windows. ReactOS is an operating system that is compatible with Microsoft Windows applications and drivers. Some of the reasons are the same as the reasons for developing Linux (an open-source UNIX clone)? In short, Linux is a great operating system, but it is not the answer for everybody. There are a lot of people that like Microsoft Windows, but are very frustrated with Microsoft's policies on various issues.

The 9x family of Microsoft Windows is based on DOS, and shares many of its weaknesses, which is the primary reason why Microsoft Windows has such a bad name. The Microsoft Windows NT family of Windows, however, has a solid design. Not everything is perfect, but without access to the source code, there is no way to fix it, so a compatible operating system must be built from the ground up.

Why don't you help develop Wine/Linux instead?

ReactOS works very closely with Wine, and thus both projects actually benefit from each other. We have several developers in both the WINE and ReactOS projects that work on cross-compatibility issues between the two projects.

It is our view that Linux + Wine can never be a full replacement for Microsoft(R) Windows(R). ReactOS has the potential for a much higher degree of compatibility - especially for Microsoft(R) Windows(R) drivers - which WINE does not address.

Why don't you help the Wine project instead?

Actually we work very closely with the Wine project. Wine probably has a lot more in common with ReactOS than with Linux. The Wine project has the goal of implementing the entire windows API on top of WineServer. There are only a few WINE dlls that cannot be used in ReactOS. These are Ntdll.dll, User32.dll, Kernel32.dll, Gdi32.dll, and Advapi32.dll. The rest of WINE's DLLs can be shared with ReactOS. We have several developers in both the WINE and ReactOS projects that work on cross-compatibility issues between the two projects. It is our view that Linux + Wine can never be a full replacement for Microsoft(R) Windows(R). ReactOS has the potential for a much higher degree of compatibility - especially for Microsoft(R) Windows(R) drivers - which WINE does not address.

Where can I download ReactOS?

Please visit the download page.

How can I contribute to ReactOS?

Please visit the contribute to ReactOS page.

  • We need coordinated testers, which means we need people that help us testing in a coordinated way.

To join our testing come to the IRC channels. Find me or any dev, we are some, and ask us what to test, everyday we have different needs so testing is not boring but different

  • We need coordinated translators.
  • We need coordinated designers.
  • We need coordinated developers.
  • We need coordinated bloggers

To find your place just come and join the IRC channels. See you there

I don't know how to code... How can I help?

We are always testing something. Just come to IRC and ask for something to be tested. We will give you some RosWork accordingly to your skills. The "I don't know how to code" is the preferred excuse followed by the "I don't have time" or "Each time I test ReactOS god kills a kitty".

I know how to code.... How can I help?

If you are a Dev, then join IRC and ask any doubts about our code, find a place in ReactOS to work, you can select any, but first contact and tell us. Maybe other Devs are currently working in that particular area. "Less time wasted when efforts coordinated!"-Yoda said.

I don't know how to code but I want to learn. How?

Study C, C++, WinAPI, then read books as "Windows Internals" and/or "Operating System Concepts". Come and ask us. For C and C++ questions you have the C and C++ irc channels, they will solve your doubts much faster.

What can I do to help?

We're always looking for either coders or testers. We're especially in need of people who know how to write NT drivers, cause our current drivers could use some improvement.

Testing on real hw is especially important as the kernel rewrite approaches completion. Some issues are known, such as missing assembly code and broken implementations causing issues on certain processors. Bugs found in trunk can be reported in Bugzilla, but try to avoid entering duplicate bugs.

Who should I talk to about helping ReactOS?

The best way to get in touch with a developer is to hop onto the irc channel.

A list of the developers, their IRC nicks, and their respective fields is here:

Note: If you have a question, don't first ask to ask the question. Just ask the question and if someone knows the answer, they'll usually answer. If you want a specific developer, ping them and then ask the question.

Others will be added as I figure out what they do.

Another way is to join the ROS-dev mailing list:

When will ReactOS be done?

First you need to define what ReactOS should be capable of when it is to be considered done. Since this definition may vary greatly between people, this question cannot be completely answered. One thing is for sure: ReactOS will continue to be developed, as there will always be a need for improvements. For more information, visit the Roadmap page.

I want to test ReactOS without risking my existing hardware/installations. Can I test ReactOS another way?

Yes, you can test ReactOS on virtual hardware. You can test it in Qemu, for which there are official packages available on the download page. This way, you can start ReactOS in a window without leaving your operating system. However, because Qemu is an emulator, ReactOS will run much slower than it would if it were running on actual hardware. Other virtual machines/x86 emulators should be able to run ReactOS as well, and ReactOS is known to run in at least Bochs, VMWare, VirtualPC and QEMU. If you know of other virtual machines that support it, please send an e-mail to the ros-dev mailing list.

Is ReactOS able to run Windows apps and Windows drivers? How about Windows Vista/7 programs and drivers?

Yes. ReactOS is able to load Windows apps and Windows drivers without hacking them. Remember: we are still in the Alpha stage so we have a big walk until reaching these objectives. You can visit our Software and Hardware Compatibility databases to know which Drivers and Apps are compatible with the latest ReactOS version.

The original target for ReactOS, with regards to driver and application compatibility, was Microsoft Windows NT 4.0. Since then, Microsoft Windows 2000, XP, 2003 Server, and Vista have been released. All these are descendants of Windows NT. As such we can gradually shift our compatibility target without worrying about the architecture changing too much. In fact, internally, Windows 2000 reports version information as Windows 5.0, XP as Windows 5.1, 2003 Server as Windows 5.2, and Vista as Windows 6.0. The ReactOS team currently targets Windows 2003 Server as the official compatibility target. Of the current releases, 2003 Server has proven one of the most robust. This does not mean that features present in later versions of Windows NT based operating systems will not be implemented in ReactOS and work is continually done to implement newer APIs.

Can I install ReactOS from a pendrive/stick?

There is no known way to install ReactOS from pendrive/stick. Any method relies in ReactOS installing itself, so it needs USB support to accomplish the task. ReactOS doesn't have USB support so:

  • Use a CD-RW instead, or a normal CD
  • May have recently changed (USB branch merged into trunk)

My screen turns black when loading ReactOS. I don't see anything.

It seems your video card is not yet compatible with ReactOS, search our Hardware Compatibility Database to find a compatible one. Also report yours as not compatible, it will help others. Share your findings!

Does ReactOS have a POSIX subsystem?

  • We currently don't have a POSIX subsystem. Well, we have one but it's broken and it's not a priority in terms of compatibility. After all, we're trying to run Windows programs here, not POSIX programs.
  • Think first: ReactOS should be stable and support a good deal of windows apps. Then worry about POSIX/*NIX, Mac, WinCe, OS/2, RiscOS, whatever else...

I inserted the Installation CD but the installation doesn't begin

Maybe your CD/DVD is a SATA device that Uniata doesn't support yet. (So neither ReactOS). If your CD/DVD is ATA then try the next trick:

OPTIONAL STEP( backing up): 1)Back up uniata.sys as uniataB_UP.sys. 2)Back up atapi.sys as atapiB_UP.sys

REPLACING 3)Rename uniata.sys to atapi2.sys 4)Rename atapi.sys to uniata.sys 5)Rename atapi2.sys to atapi.sys

If you mess the files/get lost when replacing, you can use the backep up files from the Optional Step.

The installation hangs or hangs before reaching the Desktop

Try the "I inserted the Installation CD but the installation doesn't begin" trick if your HDD is an ATA device. Remember that trick doesn't work at all with SATA devices.

When is 0.4 appearing? And Beta? And 1.0? And 123.0? And...

It depends. We need Devs and Testers (Coordinated Testers). Last statistic says 99.99% of the forum users who ask these questions has never helped in a Coordinated Testing. So stop asking and use that time to help us , if you want it asap then contribute a little. Money is appreciated but testing is much more useful at current stage.

We perform several Coordinated Testings via IRC. Join them and you will discover the feelings of being part of the Community, not just part of the Forum.

Why there is no Roadmap?

An OS covers a wide area of knowledge, it is not an App, it is a whole,-in-the-way-to-become-awesome OS. So we need devs from all the areas, it's not easy to find skilled devs, and also they are not paid, they have their real-life-work, families and problems. So no, we can't press them to work in a particular area. We can just thank them for dedicating some time to make this OS become a reality.

Developer FAQ


What language do you guys use?

C and assembly, with very little C++ for some included programs. In the OS itself, only C and assembly is allowed.

Why only C and assembly?

The reasoning is actually because of the tools we use. GCC's C++ compiler is less than stellar so we limit things to C and assembly to make our lives easier.

---How do I get ReactOS' source code and build it?---

This information is covered on this page: Build Envionment

The recommended build environment is the RosBE. It's designed to run on Windows and *nix, though the *nix version may not be as up to date as the Windows version.

---Is there any kind of coding style that is expected?---

See Coding Style

How will you avoid the inevitable "Microsoft" text throughout ReactOS?

We believe that this falls under fair use. It is also not needed except in the registry.

Will drivers designed for Windows work on ReactOS?

Some drivers have been known to work, but at this point there is no definitive answer as some facilities in kernel land that are unimplemented.

What do I need to compile ReactOS from sources?

Refer to our [[Build_Environment|Build Environment page] for information on how to compile ReactOS from the source.

What IDE should I use to develop for ReactOS?

See using an IDE for information on supported code editors.

What about so-called SEH-problem?

Structured exception handling (SEH) is used in programming ReactOS as it is used in programming for OS/2 or Microsoft(R) Windows(R) NT. SEH is a game wich is played between OS and Compiler (Keywords: __try, __except, __finally). ReactOS itself is SEH-aware and provides the infrastructure. However up till now, the used GNU-compiler is not capable of generating SEH aware code. So one can't compile a driver or program which uses SEH with the GNU-Compiler.

Graphics Subsystem

Why is the graphics subsystem not in Ring 3 but in Ring 0?

The short answer is that because Microsoft has done it this way, and we aim for driver compatibility, we have to do it the same way.

Why did Microsoft put the GUI in Ring 0?

Because this gives quite an advantage in speed. Contrary to a GUI-server, which will run in its own process, there are no context changes necessary when performing GUI operations. This does make the architecture less clean of course, and when the GUI crashes, the whole system crashes. The same discussion took place in Redmond, when the GUI went into the kernel in Microsoft(R) Windows(R) NT 4.0. They came to the conclusion that the GUI has matured, so that nothing will go wrong unless a faulty driver is present, and that the consequences are similar to when something goes wrong in user mode.

Does ReactOS have the same security problems as Microsoft(R) Windows(R)?

Microsoft(R) Windows(R) NT and successors aren't really inherently insecure systems. We believe that Microsoft made a secure system insecure as a result of some poor decisions. For example, Windows XP gives every user Administrator rights by default. Some services are poorly implemented and ease of use often takes priority over security. We can, however, rearrange these priorities in ReactOS. What will be problematic is that Microsoft hasn't pressured software creators to let their products run with normal user rights.


How do I trace an unhandled exception in user mode?

The trace looks something like this: (KERNEL32:process/create.c:328) Process terminated abnormally due to unhandled exception (KERNEL32:process/create.c:329) Address: 761a13e0 (KERNEL32:process/create.c:334) Frames: (KERNEL32:process/create.c:338) 761a2be9 Look at ReactOS/baseaddress.cfg, find the nearest lower address that matches the address you're trying to trace. Open the .map file for the corresponding DLL in viewer and search for the offset.

See Also

ReactOS User FAQ

ReactOS Developer FAQ

ReactOS Forum FAQ

ReactOS Forum Developer FAQ