Please pardon a visitor to your corner of the forum asking a silly question but, does Leopard even use all 8 cores in a Mac Pro and does current software make use of them. Say like iLife and iWork and even Office 2008? Thanks for your indulgence.
It depends entirely on the software. In order for the software to take advantage of more than one core, it needs to be threaded. In real simple terms, think of threading like multi-processing,
within a process.
For instance, a multi-processing operating system can run several processes (applications) at once. Like, say, Safari, Final Cut, QuickTime, Mail, etc.
A threaded process (application) can do several different things at once. For instance, QuickTime saving a video while it's opening and playing another and downloading a third.
Does that make sense? In order for an application (let's use Final Cut Express as our example) to take advantage of all 8 cores, it would need to be written with threads in mind. So it could spin off a thread to spool video from tape, while another thread was working on encoding a previous video, while another thread works on editing the current one. That sort of thing.
The problem is: threading is hard. Sometimes: very, very hard. It makes writing applications very difficult, depending on how tricky the app already is. And, if we return to our example: FCE is not threaded well. If you perform what it considers a CPU-intensive task, it will prevent you from doing anything else with it. And, quite frankly, that sucks.
QuickTime Pro, on the other hand, will flatline all 8 cores if you want it to. I was encoding two MPEG4s the other night, and my 8 CPUs were all at 100%. That's good threading.
The OS makes it possible for applications to take advantage of all of the cores. But ultimately, it's up to the application to do so. That's the case with any threaded operating system.
jas