Hi Toxe, It's the operating system for sure. OS10.x will recognize dual processors and perform the multi-threading operations that allow each processor to work indepndently; OS9.x will not - even operating in classic mode within OSX. It's worth it to make the jump to OSX. I've been running without any issues of note for 9 months... The best part of OSX is that you can start a render in Carrara and then go work in Photoshop, InDesign or Quark without any problems while the render grinds away! :) Mark