Not all 8 cores being used

So I just purchased an 8core mac pro a few weeks ago and installed matlab and mathematica on it. I do some intense simulations and calculations with it. When i go to activity monitor to see the usage of all 8 cores, it only seems that only one is doing all the work while the others sit idle. How can i utilize the rest of the 7 cores? Do i need more memory? Thanks

Is this using Windows or OSX?

It could be a software issue. Is the software written for a single core or is it multithreaded to use all 8?
You would only need more RAM if you actually run out of it.

im running osx. and the mathematica version i have is for 32-bit. is that why?

G4 Power Macs had dual processors that were only 32 bit. I don't think that is the cause but I could be wrong.

Not all "intense" tasks can be split up eight ways. And even those that can may have to be tweaked to do so.

http://support.wolfram.com/mathematica/systems/allplatforms/multipleprocessors.html

cool thanks for the help. i'll try it out