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2013 Mac Pro: Choosing the CPU
Apple’s dual-model sales presentation is oddly bifurcated because the base quad-core model can be up-configured to any choice of CPU and GPU. In short:
- Base 4-core model comes with 12GB and dual AMD FirePro D300 GPUs.
- The 6-core model up-configures to 16GB memory and dual AMD FirePro D500 GPUS.
- Either model can choose any CPU and either model can go with higher-spec GPUs.
Which CPU is right for your needs?
For many users, 6 CPU cores is the sweet spot in offering the best price/performance along with the next faster GPU speed. Programs like Adobe Photoshop Lightroom and Photoshop make use of 6 - 8 cores better than ever in the latest 2014 "CC" versions.
Given the reduction in CPU clock speed, the 8-core CPU appears at first glance less attractive for all-around use than the 6-core model, and the 12-core model is even less attractive. However (see discussion that follows), Turbo Boost mitigates that initial assumption and if the workflow involves more cores, those extra cores can pay off.
The 12-core models is aimed at video processing, or specialty tasks where all cores are fully utilized, and are best paired with the fastest GPUs for those who really do intensive video work.
|CPU Cores||Clock Speed||Cache Memory||Mainstream Task Speed*||Core-Friendly Speed**||Comments|
|Intel® Xeon® Processor E5 v2 Family||Higher numbers are faster|
|4||3.7 GHz ES-1620
+37% / +5.7%
||Fastest for general use due to highest clock speed, but many operations in programs like Adobe Photoshop Lightroom or Photoshop will be slower than with 6-core or 8-core options—and others will be faster! It all depends.|
~ 5.6 ±
|3.5 GHz E5-1650
+30% / + 16%
|14.0||18.9||About 5% slower than the 4-core in clock speed, but the two extra CPU cores are WELL worth it for programs like Adobe Photoshop Lightroom. Best all-around solution.|
|3.0 GHz E5-2690
|12.0||19.2||With a 14% drop in clock speed, the 8-core model is not likely to outperform the 6-core model for most tasks, but it has more cache memory and this might mitigate the clock speed losses. And it’s a good middle ground for workflows which mix video with other tasks.|
|2.7 GHz E5-2697
|10.8||22.7||Appropriate mainly for video users, but other workflows can benefit if the tasks use all cores frequently.|
* Ordinary Task Speed = expected speed with mainstream tasks which typically use four CPU cores or fewer and rarely more except for brief spikes.
** Core-Friendly = Estimated real-world best-case performance taking into account clock speed and CPU cores, application multi-threading efficiency, memory contention.
± Taking clock speed into account, the equivalent number of 3.7 GHz CPU cores (multiplier of # of cores times the clock speed). This does not take the inevitable multi-core overhead into account (hardware and software factor), which degrades performance as the number of CPU cores increases.
The processor’s rated frequency assumes that all execution cores are running an application at the thermal design power (TDP). However, under typical operation, not all cores are active. Therefore most applications are consuming less than the TDP at the rated frequency.
To take advantage of the available TDP headroom, the active cores can increase their operating frequency. To determine the highest performance frequency amongst active cores, the processor takes the following into consideration:
• The number of cores operating in the C0 state.
• The estimated current consumption.
• The estimated power consumption.
• The die temperature.
Any of these factors can affect the maximum frequency for a given workload. If the power, current, or thermal limit is reached, the processor will automatically reduce the frequency to stay with its TDP limit.
Speeds noted here might be off slightly and can be subject to thermal load which exceed TDP (thermal design power), which will reduce clock speed from top rating.
Suppose that a task uses only 4 cores. In that case, the 4/6/8 core models should all perform similarly, except that the 8-core CPU has twice the cache of the 6-core and 2.5X the cache of the 4-core, so it might be expected to outperform on some tasks (and it won’t matter for many).
With 6 cores utilized, the 6-core CPU is a smidgen faster than the 8-core, but the 8-core has that extra cache, so it all depends on the task.
If the software can really use 7 or 8 cores with no efficiency loss (not a given!), then the 8-core wins. The 12-core needs to see 9 cores used to gain parity with the 8-core CPU (12 core has a slower clock speed). The 12-core is thus appropriate only for workflows that regularly use all 12 cores for extended periods.
In short, it all depends on the number of cores. But perhaps far more important, how efficiently written the software is! Many common tasks use only a single core, and some common tasks in Photoshop use only 2-3 cores. It all depends.
That’s a bit hard to grok, so let’s look at a graph of cores and clock speeds. The thick green line at top is the 3.3 GHz 8-core CPU, which offers the best performance up to 4 cores, then is just a notch slower than the 3.7 GHz 6-core at 5/6 cores, but that performance holds out to 7/8 cores
Thus, the 3.3 GHz 8-core is the ideal CPU for mixed workloads where some top-end grunt is desired on top of fast performance for everyday tasks that are mostly single-threaded (the 3.4 GHz 8-core is rated for workstation used and has +20W power dissipation and has identical clock speeds with Turbo Boost).
The next best part is the 3.7 GHz 6-core.
See the GPU discussion page.
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