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2013 Mac Pro: How Many Cores for Your Workflow?
Here at MPG, primary use of the Mac Pro is for intensive digital photography work. Essential to that work has been ample memory along with an ultra-fast SSD so that saving and opening huge files takes seconds instead of minutes.
What remains after ensuring memory and fast I/O is how fast the CPU can get the job done, e.g., the time spent in Photoshop doing useful work.
A troubling issue for workflow efficiency is that the very design of Photoshop precludes doing useful things in parallel, like sharpening or blurring 10 layers with one command. Sometimes a script can address this, but that takes extra work to understand and develop. That sort of thing is where the real speedups could occur, but Adobe has to fix Photoshop for that: why can’t a user select 10 layers and invoke Smart Sharpen?
Common tasks can be short-lived
NOTE: Photoshop Creative Cloud offers much superior CPU core usage over prior versions. 6 cores are strongly recommended over 4, and the D500 GPUs over the D300 GPUs are likely to pay off.
For common tasks like Smart Sharpen, Gaussian Blur, Image Resize, etc, Photoshop varies in its CPU core usage, but these tasks are generally short-lived for even fairly large files, and so the clock-time savings can be modest. However, something like Smart Sharpen on large files benefits greatly from more cores and for images of 24 megapixels on up one is likely to notice lag time, which is an interactive productivity issue.
Moreover, recent developments (Jan 2014) show huge gains with new GPU support; the landscape was fluid as this was written.
A 4-core CPU with a fast clock speed can perform exceedingly well for many users, e.g. a 3.7 GHz 4-core Mac Pro or iMac or similar. But for larger files, consider 6 cores the minimum for all around work.
Longer running tasks
Some tasks use more CPU cores and/or use the GPU(s).
If compute-intensive operations (utilizing many cores) are used frequently in the workflow, then they can matter a lot, because saving 20% of a minute is a lot more than saving 20% of 2 seconds.
For such work, an 8-core running at 3.3 GHz (Turbo Boost 4.0 GHz) is better than even a 6-core at 3.7 GHz.
So how many cores?
Intensive video work is best done with 12 cores. It is a special case situation.
For photography, testing shows that 6 cores is the sweet spot, along with the D500 or D700 GPU option. The value of the high-end GPUs being dependent on particular workflow and the promise of future development.
Testing also suggests that an 8-core at 3.0 GHz is likely to perform no better than the 6-core on the vast majority of tasks.
How to decide on CPU cores?
Keep the Activity Monitor CPU history window during your usual workflow so that the CPU usage over time can be observed while work is in progress.