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iMac Pro: Downclocked CPUs

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?.

Also: Turbo Boost and the Intel Xeon W CPUs in the Apple iMac Pro.

Any photographer using a Mac is surely thinking “what about that new iMac Pro?”.

Update 23 Dec 2017: it remains a mystery as to why Apple is using downclocked Intel Xeon W CPUs in the 2017 iMac Pro. It doesn’t look to be TPD (total power dissipation) since all the CPUs have the same TDP.

I hope that I am quite mistaken about what follows. That would be wonderful. But so far all the evidence I’ve seen suggests that assuming that the iMac Pro is the best choice is a bad idea. It comes down to specific types of work with specific tasks in specific software. In other words:

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

I will be testing the iMac Pro against the 2017 iMac 5K as soon as I can get one. But I can’t outlay $8K to buy one, so it will have to be a loaner, which means I won’t be able to do it immediately.

From a reader (and I’ve received other info too):

If you look at how the hexacore i7-8700K performs (and that's the CPU slated for the next iMac 5K refresh,) you'll see that it's faster than the 8-core iMac Pro.

In fact, the 2017 iMac 5K is faster than the 8-core iMac Pro in single-threaded performance, and is about very close in terms of multi-threaded performance.

So looks like come 2018, one will be able to choose between a $5K 8-core iMac Pro with non-user-upgradable, crazy expensive RAM, scoring about 23,500 on Geekbench, and a $3k 6-core 27" iMac, with user-upgradable RAM, scoring about 30,000.

If you configure the iMac Pro with 64GB of RAM, I'll bet it'll cost at least $5.5k, and the iMac will be about $3.5k with 64GB of OWC RAM. So you'll be getting 20% lower multi-threaded CPU performance for nearly 60% more money. Unless you really need the faster graphics, ECC memory, or more TB3 ports, choosing the iMac 5K will be a no-brainer.

MPG: based on what I’ve seen, I concur, except on price: it may well but significantly higher than stated above for the iMac Pro.

Those who use specialized applications will see superior performance with a small set of applications on a subset of tasks in those applications, by virtue of more cores and faster GPU. If these are long running tasks that use all CPU cores, then it’s a huge win and the iMac Pro offers huge value.

If brief spikes using multi-core or single threaded (as with my own work), it has nil benefit with very poor value. Most people, including me with heavy duty Photoshop work, will on average see no benefit because Photoshop uses few 1 or 2 CPU cores for most everything I do. So the iMac Pro might even slow down my work, though one task I am sure it will speed up. Is that worth $4000 more?

What Apple has done is to 'spin' form over function as top-notch engineering for heat management. By designing too small an enclosure (very poor decision for heat removal) it then became necessary to use top-notch engineering to deal with the heat problem which would not exist if a proper-sized case had been used. And that would make the iMac Pro less svelte—and form takes precedence over function. The disappointing kicker is to realize that Apple is using downclocked (slower) CPUs because the faster ones would generate too much heat because the decision was made to make a too-small enclosure for the iMac Pro and/or not to size up the venting and fans. Gorgeous engineering visually (!), but impaired performance and non-upgradeable memory.

It’s a shame to have to choose faster for tasks A/B/C but slower for tasks X/Y/Z. Compromising the fundamental purpose of a tool is not elegance, and never can be.

Gaping hole in respect for professionals who want to plan around the iMac Pro along with
impaired performance to stay within a form-over-function case design


CLICK TO VIEW: Configuring my 2017 iMac 5K and Various


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