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For a 200MHz Pentium (this is an old review), the testers tried sending one billion interrupts with a latency check. When they required 8 microsecond latency, they missed one interrupt in a billion. When they only needed 10ms latency, they didn't lose any.

Comparable figures are available for various real-time Linux systems. Note that these figures are for a 650MHz CPU. The times are slightly better than for QNX, but the CPU is 3x faster.

Bear in mind that "RTLinux" programs aren't running under Linux. They're running below Linux. They can't make most system calls, for example. QNX programs are ordinary programs, and can make system calls.

The Linux 2.6 kernel isn't bad, though. Running real-time with millisecond response as high-priority Linux threads can actually work in 2.6. In 2.4, no way. You have to be very careful not to load any high-latency drivers, though.

The April 30th 2003 Slashdot article links to a more technical, well written Dr. Dobbs article about the HP 2000C's date-exiry chipped carts from...September 2002! Oh, what the hell, here's a link for the lazy:

http://www.ddjembedded.com/resources/articles/2002 /0209k/0209k.htm

The preemptive kernel work has made the user-space real time variants of Linux, like Hard Hat Linux from MonteVista, more competitive. Vendors now claim worst-case interrupt latencies under 1ms, which is far better than it used to be. But they usually mean interrupt latency for kernel-mode drivers, not response time for user programs. QNX can provide worst case hard real time interrupt response to a user program in well under 1ms. Direct interrupt response is far better. See this benchmark in Dr. Dobbs Journal, demonstrating worst case 8 microsecond (not millisecond) latency over hours of testing on a 200MHz computer.

Linux is getting better at real time. Two years ago it was a joke.

You can download the free version of QNX here. This is for desktop PCs. The cross-compilers and kernels for embedded systems cost money. It's a cute little desktop OS. Even runs Mozilla.

Ed Nisley had reviewed this in Dr. Dobb's Journal. The review is available here. I had just read the article this morning and was pleasently surprised to see the review here.

I have nothing to contribute to this question but I honestly wonder if it was inspired by the article in this month's issue of DDJ where they talk about the battery life of PDAs.

Article about the dangers of car PC's and cell phones use while driving.

Instead of just talking on their cell phones while driving, they can watch video on their cell phones while driving. Oh joy. Oh rapture. Oh ecstasy.

Check out this article as well as others at ddj embedded site

Check out this article as well as others at ddj embedded site