Comment Re:Riiiiight. (Score 4, Insightful) 233
Yes, QNX has been around for a long time.
\What most people don't get is what a realtime OS is, and why it matters. Other multitasking OSes are generally "best-effort" OSes, but in a realtime OS, the whole scheduling system is based on giving guarantees, making sure that things happen within a certain time frame or a certain order.
The overhead is huge, which is why you don't se RT on any normal desktops or servers, but in something like a car, airplane or hospital device, you would rather know that 100% of the requests get served in 100 ms, than having an average time of 10 ms, but a worst case time of 1000+ ms.
If you know the worst case, you can program your systems to operate within them.
Linux does have a RT version, in part supported by Ingo Molnar and Theodore Ts'o, but it does not see heavy use. In part, this has been because for a realtime OS to be successful, all the parts have to play ball, not just some. And in part it is because a realtime OS is quite a bit slower on average, and most regular users would rather have improved average speeds than improved worst-case.
But for a car? Give me a realtime OS any day. I don't want traction control to cut in a tenth of a second too late because the kernel was busy doing garbage collection, time synchronization, and handling an urgent warning that the oil temperature was too high.