Mac Pro: How Many CPU Cores?

2011-02-04 • SEND FEEDBACK |
Related: CPU cores, Mac Pro, memory

To test my tests, I’ve swapped the CPU trays between my 12-core and 6-core Mac Pros, both running at 3.33GHz (my 12-core has been upgraded to be faster than any Mac Pro 12-core by Apple). I spent the day working as usual.

The result: I can’t tell any difference running my 6-core 3.33GHz instead of my 12-core 3.33GHz, unless the 6-core is slightly snappier. That’s normal, notwithstanding the cpu-envy drool you can read online all too often. Save your money, unless you have a proven need for more cores. Or have me help you decide.

See my list of recommended Macs and displays, and of course upgrade your stuff at OWC. Thanks for using those links so I get credit. And when you get an MPG Pro Workstation, you’ll be advised if your choice seems inappropriate for your stated purposes.

Software and cores

Unless software is very well written, it not only won’t use more than 6 cores well, it might actually incur program overhead that drops performance below that of a machine with fewer cores (synchronization, extra memory demands, etc) .

Very few programs use more than 6 cores efficiently (it’s not just cores used, it’s task time reduction that counts). Which leads us to the following general statements:

An 8-core 2.4GHz machine is the worst possible choice for most users. Because those cores go wasted, and the clock speed is slooooow.

A 6-core 3.33GHz machine is a superb choice for most every user (but also more than really needed for many applications).

A 12-core machine is best only for computing chores that have time-consuming jobs to crunch, and software that uses more than 6 cores effectively. Or when 48GB or 64GB memory is required to keep data in memory (the one exception for the 8-core 2.4GHz).

Learning more

If you study my in-depth review of the current Mac Pro, including the large number of performance tests, you’ll soon see that more cores can be slower. Usually not, but sometimes it happens; it’s software-dependent.

Another mundane reason that 12 cores don’t necessarily run faster than 6 cores is that Apple’s 12-core runs at 2.93GHz, whereas the 6-core runs 13% faster at 3.33Ghz, which makes the 6-core a 6.8-core machine in terms of equivalent clock speed. But with less program overhead.

Cores and clock speed interact on any particular task