A multi-tasking operating system for the x86 32-bit PC architecture

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Frequently Asked Questions

This page provides a answers to a few of the questions frequently asked about XOS. If you don't find your question here (which is likely, since the list is currently pretty short), please send it to and we will probably add it to this page.

What is XOS good for?

XOS is targeted at various embedded or dedicated applications. It provides a full featured multitasking environment which has a very small footprint. It is a relitively simple system which can reasonably be well enough understood to provide assurance that the system is really doing what it is intended to do and nothing else. The fact that it provides a non-standard execution environment is actually a major advantage in many dedicated applications. For example, if a PC is used as a POS (point of sale) terminal, you do not want games and other programs downloaded and run on that machine.

Do we really need yet another OS?

We think so. We believe that most available operating systems have increased in complexity to the point that they are not really understandable by any one person. We believe this level of understanding is necessary if a system is to be really secure. The goal of XOS development is to "Keep It Simple" while still providing reasonable functionality.

How is XOS different from Linux?

One word: simplicity. Over the past few years the standard Linux distributions have grown more and more complex, making it progressively more difficult to use Linux as the basis for a system that can be fully understood. We believe this unnecessary complexity makes it very difficult if not impossible to create a really secure system using Linux. While XOS lacks some of the more esoteric capabilities of Linux, we believe it is a better choice for those applications it can support.

What hardware does XOS support?

XOS should run on any "standard" x86 PC with a Pentinum class processor and at least 2 to 4MB (yes, that's MB) of RAM. Use of graphics mode programs requires that the console display support the version 3.0 real mode VESA BIOS functions. XOS's sound support requires HDA audio. We have tried XOS on numerous PCs with almost complete success. We have had problems with some different (not RTL888) HDA codecs and have found at least one several year old motherboard whose OHCI fails at startup. We have not found any Pentium class CPU chips that don't work with XOS. (As far as we know, it's never been tried on a Transmeta chip, but that's probably not very important now!)

Does XOS support "legacy free" PCs?

Yes. XOS has been run extensively on an Asus EeeBox, which has no legacy devices except for an emulated IDE controller (which XOS requires for hard disk access).

Does XOS support multiple CPUs?

No, XOS does not currently support multiple CPUs. We have felt that, given the intended uses for XOS, this is not worth the resources that would be required to implement. However, we may look at this again at some point. Fortunately, all of the current multi-core chips work fine as a single CPU chip and thus work fine with XOS in that mode.

Is there a 64-bit version of XOS?

No, there is no 64-bit version of XOS. We do see an eventual need for this and hope to provide it at some point. Unfortunately, our choice of OpenWatcom as the XOS C compilier creates problems here since OpenWatcom can not generate 64-bit code and so far OpenWatcom has not committed to adding this. We will have to: 1) Wait for OpenWatcom, 2) Upgrade the OpenWatcom compilier ourselves, or 3) Find another 64-bit C compiler (maybe gcc?).

Why is there so much assembler code in XOS?

XOS was originally written when the only 32-bit x86 CPU in existence was a 16MHz 80386 and a "large" system had 1MB of RAM! Given this, it was felt that efficiency was extremely important. Thus all kernel level code was written in 80386 assembler. The situation today is quite different and we are currently in the process of rewriting virtually all of the assmebler code in C. Providing an exec mode execution enviroment that would support code written in C was one of the main changes between versions 3 and 4. This project is on the order of 15 to 20% complete and is continuing.

Does XOS support a C++ compiler?

Not at present. We have not needed one for the projects we are currently working on so have not taken the time to port the OpenWatcom C++ compiler. Given that it is written in C and runs in the same environment as the C compiler, this should be a reasonably simple task.

Is XOS really free?

Yes. All XOS code and documentation is in the public domain and can be freely downloaded and used however you want as long as you agree not to hold the authors responsible for what you do with it. You should note that XOS is NOT intended for life-critical applications. Some features of XOS (mainly graphic mode support) use external freeware packages which have somewhat more restrictive terms. None of them, however, are under the GPL or any other license that makes any "contamination" claims. Please see the Legal page for details.

Is support available for commercial use of XOS?

There is currently no formal support program for XOS. However, if you are considering XOS for a commercial application and would be interested in some level of paid support, please contact us.



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