A stupid question about smp:

I wonder why some programs use only one core with 100% load while the second core does nearly nothing.
Sometimes the working core changes but still only one does the main work.
On the other hand there are programs distibuting the load balanced to both cores.

If every one processor instruction is dependent on the result of previous one's execution - is there any point of multiple cores executing them?
All I'm trying to say is that not only kernel have to be made for multi-core system but the software too, more or less.

So the software has to be programmed to execute on multi cores. Is that right?

Well, yes.

Yes and no. The program must use several threads or execution flows for it to be able to take advantage of a multiprocessor system. Each processor (or core in this case) executes one thread at a time, changing the executing thread from time to time. If a program only has one thread (this is a very common case), it will be running in one of the processors. If, however, a program uses several threads, they can be run on different processors at the same time. You can have a multithreaded program running on a single processor, though, so it doesn't need to be programmed specifically to take advantage of multiple processors or cores. The OS takes care of that.

OK, I understand. Thanks for your answers and for being not too scientific ;-)