do multiple instances on Apple OS X use different CPU cores?

I have an Apple Mac Pro with 6 cores. I finally figured out how to run 2 instances of Matlab (the right-click "open additional instances" wasn't working but I managed to run 2 copies from Terminal). Question: do the two instances automatically use different CPU cores? That is, running 2 instances simultaneously on a 6-core machine is likely to be faster than one at a time (sequentially), or do they just end up sharing 1 processor and not giving me any speed advantage?

[Guillaume]

I'm not familiar with OS X but generally it's the OS that controls allocation of program to virtual or physical cores, not the program itself.

Answer 1

[Faiz Gouri]

It is completely bound by OS scheduling algorithm. Running multiple MATLAB instances is like running independent processes You can try set processor affinity if you want to run Matlab on different cores, but that might not necessarily result in improved performance. Moreover, OSX does not provide process affinity. You can do Thread Affinity though, which is not useful in your use case.