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iMac Pro: Pricing and Thoughts

Recently I bought a 2017 iMac 5K for solid reasons and yesterday I discussed the switchover and the gear I’m using.

See also Wither the iMac Pro? and 4-Core CPUs do not Leave Much Grunt for Other Tasks and Will the iMac Pro Be Worth The Cost?.

See all iMac Pro configurations at B&H Photo.

See yesterday’s discussion, written before the pricing and specs were released, summarized as:

Question: is the iMac Pro faster or slower than the 2017 iMac 5K?
Answer: yes.

Question: will a 1000 horsepower Ferrari beat a 250 horsepower Toyota 4Runner on rocky potholed dirt roads?
Answer: yes, for up to 1/4 mile or so, then put on your hiking boots.

Note the idiocy of the 2nd Q/A pair: “most powerful Mac ever” blithely skips over the usage scenario relevancy, although the iMac Pro may well prove to be more reliable in the long run (no way to know as yet). Of course the iMac Pro is the “most powerful Mac ever”. But maybe not for what you or I do, and maybe only sometimes.

Quick points of note aimed at the vast majority of photographers

  • See Q/A above. The precise workload and mix of tasks you and only you do decides the question. Only those where 6+ CPUs are in full use are you likely to see any performance boost with the iMac Pro vs 2017 iMac 5K—and it’s probably parity at 6 cores, not superiority. So unless your CPU workloads routinely use 8 cores for a significant amount of time, you’re not winning by having 8/10/14/18 cores.
  • GPU intensive tasks are very task specific. The issue is how long the GPU is used; if it blips for half a second and it is 3 times faster in a 4 second operation, the effect is nil. If it is used intensively for 2/3/4/5 seconds, then a 3X faster GPU will rock, and make all the diference. But GPU usage is even more sensitive to exact workload.
  • If you are spending $5K plus, then in context it is foolish to buy any configuration with 32GB memory, since it is not upgradeable. 64GB memory is the sweet spot, and ample for my needs; 128GB is overkill for 99% of photographers including me.
  • When only 1 to 4 cores are used (common in my own Photoshop usage), the fastest clock speed wins, e.g., the 2017 iMac 5K has a base clock of 4.2 GHz and turbo boosts to 4.5 GHz, so none of the cores drop below 4.2 Ghz. The iMac Pro 8-core has a base clock of 3.2 GHz and turbo boosts to 4.2 GHz, the 10 core has a base clock of 3.0 Ghz and turbo boosts to 4.5 Ghz. But when more cores are used, the iMac Pro CPUs drop towards base clock speed—much lower than the 2017 iMac Pro. Hence there is some average clock speed for the number of cores used that determines which machine wins, and this is not likely to be the iMac Pro until 6+ cores are used.
  • Does 4.2 vs 4.5 Ghz matter? Not much. 4.5 vs 4.2 is 7%, which is barely noticeable. Nice but not very important.
  • How many cores are used for how long to make 8 or 10 cores worthwhile: I deem steady usage of 6+ cores the threshold just to signifiantly win over the 2017 iMac 5K, which has base clock of 4.2 Ghz for all 4 cores, whereas the turbo boost mode on the iMac Pro quickly drops as more cores are used. This is why my 2013 Mac Pro 8-core 3.3 Ghz is outrun or matched by the 4-core 2017 iMac 5K on many tasks and thus speeds up my work on most everything—the Xeon processors cannot maintain turbo boost for more than a core or two, so the base clock speed steadily drops as more cores are used. See the type of behavior in the Xeon chips in the 2013 Mac Pro in the charts and graphs in 2013 Mac Pro: Choosing the CPU.

Videographers

For videographers crunching 4K or similar footage: 18 CPU cores, 128GB memory, 4TB SSD, 16GB GPU or 14 CPU cores, 128GB memory, 4TB SSD, 16GB GPU.

Buying tips

Don’t spend thousands on stuff you do not need, and don’t skimp on stuff that cannot be upgraded and you might realistically benefit from over several years of usage. These points are generalized to the vast majority of users, including me.

  • 8-core CPU is ample for most users; the 10 core is better in theory, but real benefit with 10 cores will be modest except in specific application and task specific scenarios and total runtime savings in such scenarios might be quite modest. One specific scenario which I would benefit from (even 14 or 18 cores), is focus stacking. But the vast majority of the time I spend is retouching, where it won’t help much.
  • 64GB memory is the sweet spot; 32GB might prove a foolish decision, 128GB is overkill.
  • GPU with 8GB memory is way more than adequate, which is what my 2017 iMac 5K has. None of my work is going to run faster with 16GB GPU memory.
  • 2TB SSD is now my mandatory minimum. I’ve learned the hard way (running out of space), that 512GB was not enough (had to buy another), and last trip this fall 1TB was barely enough (almost forced to much slower external storage). That said, many users will be just fine with 1TB. The SSD is the key to keeping the CPUs busy whenever I/O is involved, so performance sensitive data has to fit onto a very fast SSD. 1TB is fine for that, but it might require organizational hassles that make it a headache to optimize.

I am unlikely to buy an iMac Pro (performance and cost reasons). But if I did, I would most likely buy either this this 8-core iMac Pro or this 10-core Mac Pro, pending some performance surprise I cannot determine and prove out as worthwhile until I test the iMac Pro.

Accessories

You’ll want Thunderbolt 3 peripherals, such as the Thunderbolt 3 version of the OWC Thunderbay 4. Many more options will be released in the next several months, so I see no hurry in ordering an iMac Pro as there will be some interesting stuff coming

Here are a bunch of Thunderbolt 3 periperhals. However, I recommend waiting until March 2018 or so before investing in expensive items if not needed immediately, because more and better choices will appear by then.

Recommended Apple iMac Pro configuration for vast majorityof photographers
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