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
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
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
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
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