Comparing Cores vs. Clock Speed (Introduction)

A Mac Pro is expensive enough to begin with, but paying more for the same performance is silly.

This special report takes a photographer’s viewpoint on the Apple Mac Pro, asking whether eight cores is really better than four.

The fastest 8-core Mac Pro to be had as of May 2010 is the Mac Pro Nehalem 2.93GHz (see the in-depth review). The 8-core model is not available at 3.33GHz, but a quad-core model is available.

Core overhead

The 3.33Ghz model has a 13% clock-speed advantage over the 8-core 2.93GHz. Thus, on the 8 core model, 4.5 cores must be utilized just to achieve the same performance, and that ignores the overhead of more CPU cores, software limitations, etc. So realistically, using 5 cores at 2.93Ghz is about the same as 4 cores on the 3.33GHz.

With Photoshop CS4/CS5, there is also increased overhead with 8 cores due to CS5 implementation weakness; it’s just not very smart about knowing how many threads are useful, so it wastes time and memory allocating too many threads for tasks that won’t even benefit from them.

The contenders

The Mac Pros tested here were MPG Pro Workstations; speed with a vanilla Mac Pro will be slower. The solid state drive setups used are so fast that they eliminate any ordinary disk activity as a factor, hard drive systems will perform at a lower level.

Note that the 8-core model entails a US$2200 upcharge over the 4-core 3.33GHz model, enough to pay for 24GB memory and a solid state drive upgrade.

Drive speed is a minor factor for most of the tests (except diglloydHuge), and two SSDs almost max-out the Mac Pro internal SATA bus, so the 2-vs-3 SSD setup is not important. The point of fast drives (SSDs) is to let the CPUs work at their fastest, without delays.

Although both machines had 2TB hard drives, all tests were done on the dual/triple SSD RAID volume, thus these results are “best obtainable”. There is no faster setup.

It is important to note that the amount of memory is not very important for most of the tests eg that the 24GB quad-core vs 48GB 8-core config doesn’t matter except for diglloydHuge.

Mac Pro Nehalem 8-core @ 2.93GHz

This is Apple’s top-of-the-line Mac Pro, further enhanced as an MPG Pro Workstation.

• 2.93 GHz dual-CPUs, 8 cores with hyperthreading (16 virtual cores);
• 48GB OWC memory as 6 X 8GB (except as noted);
• Dual OWC Mercury Extreme 200GB solid state drives as RAID -0 stripe for Boot and Scratch.
• 2TB Hitachi 7K2000 hard drives (not used for test);
• 30" NEC wide-gamut color display;

Mac Pro Nehalem 4-core @ 3.33Ghz

This is Apple’s top-of-the-line quad-core Mac Pro, further enhanced as an MPG Pro Workstation.

• 3.33 GHz CPU,4cores with hyperthreading (8 virtual cores);
• 24GB OWC memory as 3 X 8GB;
• Three OWC Mercury Extreme 200GB solid state drives as RAID -0 stripe for Boot and Scratch.
• 2TB Hitachi 7K2000 hard drives (not used for test);
• 30" NEC wide-gamut color display;