Lennart Poettering of Red Hat, PulseAudio maintainer has blogged in detail about the impact of Real-Time Group scheduling in 2.6.25 kernel. The Real time patches come from -rt patchset maintained by Ingo Molnar of Red Hat which aims to make Linux the first general purpose operating system with hard real time features. 
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Member since:2007-05-19
Yes all those links show that linux can work with *soft* real-time capability. *Hard* real-time is different as previously mentioned.
This is also why for instance linux is usually multiplexed with another RTOS for such delicate operations (e.g. modem communication on mobile phones).
Member since:2005-07-06
Some of the documents I refer specifically use the word hard real time. As an example
https://wiki.ubuntu.com/RealTime/Feisty
Red Hat MRG product has specific guarantees below certain milli seconds for specific transactions. Refer to their whitepapers for more details.
I guess your definition of hard real time is different then which is ok as long as you clearly specify what your definition is or provide some reference as to to what you believe is a commonly acceptable definition.
Within specific industries, they start out with a definition or avoid the term and just specific the guarantees just to avoid this problem. That for example guarantees the max time slice among other things.
Edited 2008-04-19 00:29 UTC
Member since:
2005-07-06
Take a look at
http://kerneltrap.org/node/11752
http://rt.wiki.kernel.org/
Hard real time cannot be achieved with the vanilla kernel but this patchset can enable that. Vendors are already shipping products based on this.
http://www.redhat.com/mrg/