Dual Processor Advantage

Dual Processors & Threads

The short answer is this...

If the programmer wrote the program in Carbon or Cocoa and used "threads", then yes, that program will benefit from multiple processors so long as there is a time in the program where two or more threads are spawned at the same time.

If the program is using only one thread (or, no threads), then you may still see a benefit because other applications on the machine (including various portions of the OS that will likely be doing something) will use the other processor.

Most modern applications use threads to some degree, or call on operating system APIs that are threaded.

There are three situations where you could see a near 100% performance increase:

1) When running two applications that were both attempting to max-out processing power. For example, running an intensive photoshop filter and compressing a movie at the same time in FCP.

2) When running an application that is very intelligently designed to split a highly-processor intensive task into multiple threads in anticipation that there may be multiple processors to serve it. You typically only see this in high-end applications where the programmers expect that they may be running on multi-processor machines.

3) Many little day-to-day things that you don't even think about. For example, when a window is getting minimized into the doc and you're running a photoshop filter. Because the minimization gets sent to the least-busy processor, you should not notice a machine slowdown when this type of thing occurs. This will generally give the box a much more "snappy" feel.

Basically, when you've got two processors, very few things actually be happening twice as fast, but a lot of things will feel faster and more responsive.

Oh! And I almost forgot...

You won't even think about iTunes slowing you down while you're working. It will happily use a nice chunk of one processor while the rest of your apps take advantage of the rest of the CPU power.

Of course, I'm not sure how much iTunes really slows down these new G4s anyway.

Can anybody tell me? How much CPU time does iTunes use while playing on a fast G4?

The Beatles "Rubber Soul" album pulls between 18-25% on my G3 400. Gosh, this machine is starting to look slow...