diglloyd Mac Performance Guide

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Mac Pro Westmere Clock Speed, Cores, and Cache

Last updated August 21, 2010 - Send Feedback

This is the most complex product offering yet offered from Apple. Never before have so many choices been made available for the Mac Pro.

Performance rarely scales perfectly with CPU cores

The 2010 hexacore 3.33GHz model has 2 more CPU cores than the 2009 3.33GH 4-core model. It also has 50% more on-chip cache memory (same amount per core). In our dreams, 6 cores would yield 50% higher performance than 4 cores. In the real world, life is not so breezy.

Most software is not written well enough to take full advantage of the extra CPU cores. Or the task itself cannot be split among cores (you cannot bake a cake 4X as fast with 4 ovens). And even well written software has some coordination overhead, so a 45% gain would be outstanding. Still, most RAW processing software is far from efficient, processing one RAW file at a time while leaving CPU cores idle.

Single-processor configurations

Single-processor models have four memory slots, for up to 32GB of memory using 8GB modules.

The 6-core 3.33GHz model is the “sweet spot” — for many tasks it should prove to be the fastest of all the models by virtue of CPU clock speed. The 2.8GHz and 3.2GHz have a slower system bus by 25%.See the test results— this matters.

All the single processor models consume 130 watts under peak load (far less when idle).

  $$$ Cores Processor Max Power
(watts)
Speed
GHz
Level 3 cache per processor Memory speed Maximum Turbo Boost
Base config $2499 4 Intel Xeon W3530 "Nehalem" 130 2.8 8MB 1066MHz 3.06GHz
Upgrade to $2899 4 Intel Xeon W3565 "Nehalem" 130 3.2 8MB 1066MHz 3.46GHz
Upgrade to $3699 6 Intel Xeon W3680 “Westmere” 130 3.33 12MB 1333MHz 3.6GHz

Dual-processor configurations

Dual-processor models have eight memory slots, for up to 64GB of memory using 8GB modules.

The 8-core 2.4GHz model is a dud for 99% of users. Skip it unless you know exactly why you want it.

  $$$ Cores Processor Max Power
(watts)
Speed
GHz
Level 3 cache per processor Memory speed Maximum Turbo Boost
Base config $3499 8 Two Intel Xeon E5620 “Westmere” 80 X 2 2.4GHz 12MB 1066Mhz 2.66GHz
Upgrade to $4999 12 Two Intel Xeon X5650 “Westmere” 95 X 2 2.66 12MB 1333MHz 3.06GHz
Upgrade to $6199 12 Two Intel Xeon X5670 “Westmere” 95 X 2 2.93 12MB 1333MHz 3.46GHz
Non-Apple upgrade from any model above $TBD 12 Two Intel Xeon X5680 “Westmere” 135 X 2 3.33 12MB 1333MHz 3.6GHz

Analysis

See the next page for performance estimates for various scenarios.

Are 12 cores faster or slower than six or eight?

Yes.

Apple’s own performance graphs show that at 2.93GHz, 12 cores are only ~30% faster than 8 cores in some cases, not the nominal 50% faster. If the price is the same or lower, then that’s a win of course.

Except for very specialized tasks, anyone with an 8-core system should not be rushing out to upgrade to a 12-core system.

Are 12 cores faster than six?

The vast majority of applications cannot even use four (4) cores effectively, let alone eight or twelve. It all depends— see the test results. Paradoxically 12 core can be slower or faster than 4 or 6 cores.

A few programs do make good use of 4–6 cores, hence a hexacore system at a faster clock speed is a better choice for most users.

A six-core 3.33Ghz processor is already ahead of a 2.93GHz processor by 13% in terms of clock speed. So it’s almost like a 7-core processor in terms of a 2.93Ghz processor (there is increasing overhead per core, so that’s a fair way to round and compare). See the test pages that follow.

Cache memory

Of particular note with the 3.33GHz hexacore model is the 12MB of on-chip cache. This cache memory helps keep the CPU cores from going idle by caching access to main memory. The other single-processor options only have 8MB of cache memory (same as the Mac Pro Nehalem). While it’s the same amount per core, if only 2-4 cores are busy, then the hexacore model has an advantage.

The new hexacore Mac Pro has the following performance enhancements over the prior quad-core Nehalem:

  • Six cores instead of four;
  • 12MB of on-chip cache instead of 8MB;
  • Faster memory speed of 1333MHz instead of 1066Mhz.

The result is a 10-15% advantage over the 3.33GHz quad-core Nehalem 2009 for most tasks. See the test pages that follow.

See also

In-depth Review of the March 2009 Mac Pro Nehalem.

Mac Pro Nehalem Shootout


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