most reliable hard realtime OS

What is considered to be the most reliable hard real time OS for 32 bit MCUs ?

Telco equipment (running real-time software) runs on Linux and Solaris and has downtime of the order of minutes per year. Of course, you should have multiple units for redundancy. You might want to read about the space shuttle computers.

Linux is very very stable for general usage, but even that is low-end of the scale when reliability is a must. In that case, better have a look at some (mostly closed source) OS'es that are actually used in safety-critical / military / aviation / aerospace / manufacturing control or similar applications. And which are designed and/or certified for such uses by respected organizations in the field. Some examples:

Integrity (used in fly-by-wire control for fighter jets & things like that)
VxWorks
LynxOS
QNX
RTEMS

As much as I like Linux, it needs significant patching for real-time use, and I doubt there exist patches to make it a hard real-time OS (kernel). Although I might be mistaken on that one as it's used in many flavors & places... :smile: At least (like Solaris) mainstream desktop/server versions are NOT. Which is not surprising as both are popular on servers, which in some respects have requirements that are opposite to (hard?) real-time use.

From a brief reseach, I see that Integrity and VxWorks lead the market as far as eliability is conserned...Is this true ?
Is there any other hard real time OS that shall be considered for systems that must be ultra reliable ?

With OS'es like the above, hardware is probably much more likely to fail than the OS that runs on it. So in practice other criteria like licensing issues, supported platforms, available applications / development tools etc would decide your choice.

shaiko said:

Is there any other hard real time OS that shall be considered for systems that must be ultra reliable ?

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You might want to check out systems based on L4 kernel family, in particular **broken link removed**. Potentially on a higher level of security than any of the above, but at this point more an academic product than something that's flown in spacecrafts... ;-) Although some L4 family members have seen use in commercial products. Not sure whether/which of those are hard real-time but if not, probably close.

**broken link removed** is a similar effort but seems to be basically dead these days.

Other than that there's a long list of real-time OS'es (many of which are open source), most of which will be more than reliable enough as long as you're not flying fighter jets...

shaiko said:

What is considered to be the most reliable hard real time OS for 32 bit MCUs ?

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What kind of project? Medical, aircraft, space, personal project, etc?
What size budget? What processor family?

Also, technically you could write your own OS (although some "experts" frown on it : ), and assuming you don't have many features (like minimal methods for process synchronization, task creation etc) and if you are running only a specific set of processes and you test it well, then reliability can be extreme. It is not unknown for internet routers to have had uptimes (i.e. no reboot time) of more than 5 years, and they are not running any commercially available OS sometimes, but a proprietary OS instead. Contrast that with your average home devices which run hot, and are less well tested, and may reboot or may have hardware failure in a few years. So, it is hard to say which is the most reliable OS since there are some which are just not commercially available.