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Assessing the Dec 2017 Apple iMac Pro

Save money on memory for all upgradeable Macs at OWC. Get iMac 5K at B&H Photo.

See also Comparing the 2017 iMac 5K to the iMac Pro.

I did not get everything I wanted, but the newly announced iMac Pro looks promising, with a monster graphics card, support for up to 128GB of ECC memory and 4 Thunderbolt 3 ports on two buses. Availability is December 2017, at least 5 months off. This pre-announcement of a specific shipping month is unprecedented for Apple (the promised Mac Pro has no shipping date).

The iMac Pro is already behind the curve, six months before it ships.

Is the iMac Pro approach merely to be a placeholder until the promised modular Mac Pro arrives in late 2018 or early 2019? Or is it a longer term offering.

Apple’s specifications for the iMac Pro leave certain details unstated (one Thunderbolt 3 bus or two, 8 bit or 10 bit color), but give us something to think on.


MPG expects that a fully-loaded iMac Pro (128GB, 18 cores, 4TB SSD, Vega 64 GPU) will run as high as $14,000. This breaks down as follows with very rough estimates based on past Apple pricing:

  • +$500 for 10 core CPU or +$2500 for 18 core CPU (maybe more, since these are XEON enterprise-grade CPUs)
  • +$800 for 64GB or +$2000 for 128GB
  • +$800 for Vega 64 GPU
  • +$800 for 2TB SSD or +$2500 for 4TB SSD (Intel Optane or conventional?)

These figures quite possibly are too low. Maybe that GPU and 18 cores running for a year can mine a few Bitcoin to soften the blow?


The sealed case shows dubious design judgment for practical usage, given that dust WILL accumulate inside the machine, which is likely to result in premature failure due to no way to clean off the dust. Particularly given the fact that an iMac Pro driven hard will need large volumes of air to keep cool. Where is the discussion of “user replaceable air filters”? See Clean Dust Off Computer Innards for Longer Service Life.

Pros love iMac. So when they asked us to build them a killer iMac, we went all in. And then we went way, way beyond, creating an iMac packed with the most staggeringly powerful collection of workstation-class graphics, processors, storage, memory, and I/O of any Mac ever. And we did it without adding a millimeter to its iconic all-in-one design.

If you work in a clean room, fine. But most of us do not and many of us have some dust or a cat or dog and Dust Happens. The iMac Pro running at full tilt is going to suck in a lot of air, and that means dust is going to start coating that $5000 to $13000 of electronic goodies. Where is the 5 year AppleCare coverage if Apple thinks this sealed design is such a great one? Why does a pro machine starting at $5000 have a laughably short 1-year warranty? If it’s such a great design, the warranty should be 5 years. But MPG doubts that an iMac Pro will survive even 3 years if used hard as a pro machine.

CPU cores

The bump from 8 to 18 cores is likely to be $2500 or so since the 18 core CPU is by itself around $2000. Since Apple needs to profit mightily, a $2000 CPU surely has to cost substantially more than Apple’s cost. Even if Apple gets a huge discount to $1000 for the 18-core CPU, that implies a $3000 upcharge when sold to the customer.

With 10 or 18 core options (8 cores by default), bragging points can be had in exchange for money. And that’s about all you’ll get for many uses: for most users, 8 CPU cores is ample, with 18 CPU cores of little use except for video users. Photoshop and Lightroom do not use even 8 CPU cores more than fractionally, so still-photo users need not concern themselves with more than 8 cores unless Adobe gets on the ball and uses cores much more efficiently between now and January 2018.

As a software developer, 18 CPU cores is appealing for testing and debugging and optimizing and general intrigue. The flip side is that most software developers do better at implementing threading bugs than using cores in a scalable fashion, and many don’t scale at all, chewing up CPU cycles but not running any faster using 8 cores than 4 (thread contention).

The emphasis on GPU support in recent years has been misguided in MPG’s view, now that 8/10/18 CPU cores are reasonably mainstream for pro users. Misguided in the sense that GPU benefits are often marginal and come with many bugs, and the emphasis on the GPU has meant de-emphasizing CPU cores. With 8/10/18 CPU cores, lack of robust (competent) support for high core counts means that few applications will be able to use 18 CPU cores in a scalable fashion (not easy to produce thread-safe code, and some algorithms are serial).

The new CPU design designates one or two overclocked CPU cores that with proper OS support can be used to make single-threaded tasks run at very high speed these one or two specially designated CPU core. So the old downside of more cores at slower clock speed may be less important with these new CPUs—if macOS supports it.

AMD Radeon Vega GPU ≠ NVIDIA

Radeon Pro Vega 56 graphics processor with 8GB of HBM2 memory, Configurable to Radeon Pro Vega 64 graphics processor with 16GB of HBM2 memory

Professional users prefer NVIDIA by 4-to-1, so this sucks from a pro user perspective.


It’s not clear if the iMac Pro memory can be upgraded—reader David B points out that the cutaway on the Apple site shows 4 internal memory DIMMS. At the least that imples a problematic upgrade process (heat gun to take off the rear case). It’s also possible that Apple will solder on the memory in shipping systems. That Apple thinks non-upgradeable is “Pro” is an incredible proposition.

In MPG’s view, the iMac Pro makes zero sense with 32GB of non-upgradeable memory (pricing starts at $5000), so that means choosing 64GB or 128GB. Given the $1400 upcharge to go from 8GB to 64GB in the regular iMac 5K, the iMac Pro might hit $7500 for a 128GB config, and that’s before a larger SSD and top-end graphics card.


The internal presumably non-upgradeable SSD starts at 1TB and can be had at 2TB and 4TB capacities. Expect to pay another $1000 or so for 2TB and $2500 for 4TB, perhaps.

Unclear is whether the SSD is Intel Optane or conventional. Since Apple makes no mention of Optane, presumably it is conventional flash memory design.

Display and color

There is no statement of whether 8 bit or 10 bit color is used, but “billions” implies 10 bit. There exists no way to true-calibrate an iMac display, there being only faux calibration.

The support for four 4K displays implies that one 8K display should be useable via two cables, since an 8K display is equivalent to four 4K displays in terms of bandwidth.

27" 5K display at 5120 X 2880 pixels with 500 nits brightness and P3 Wide Color gamut.

Simultaneously supports full native resolution on the built-in display at 1 billion colors and:

  • Two 5120‑by‑2880 (5K) external displays at 60Hz with support for 1 billion colors, or
  • Four 3840-by-2160 (4K UHD) external displays at 60Hz with support for 1 billion colors, or
  • Four 4096‑by‑2304 (4K) external displays at 60Hz with support for millions of colors
  • Support for extended desktop and video mirroring modes
  • Thunderbolt 3 digital video output
  • Native DisplayPort output over USB-C
  • VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)

Thunderbolt 3 and ports

There are four Thunderbolt 3 ports, and while not called out in the specs (weird!), the Apple presentation does confirm dual Thunderbolt 3 busses for a total I/O bandwidth equivalent to three Thunderbolt 2 busses; the 2013 Mac Pro has 3 busses, so the iMac Pro has 1/3 more I/O bandwidth and at twice the peak speed—more than ample for just about any conceivable need and supporting ultra high speed external SSDs.

The inclusion of four USB 3.2 gen 2 ports, 10 gigabit ethernet and and SDXC card slot are all very nice features so that one does not have to use up Thunderbolt 3 ports for mundane things like USB 3 devices.

Toy keyboard and mouse

MPG does not consider a wireless keyboard and mouse much more than toys on a $5K to $13K computer. Such devices have always failed in use for MPG before.

Reader comments

Andrew D writes:

I agree that overall the iMac Pro does look pretty damn good, allowing up to 18 cores, 128GB of memory, and the Thunderbolt 3 ports (although again, dependent on number of busses) is really impressive for the iMac. However, there’s a few concerns that I still see:

  • We’re still stuck with AMD as the only option for Mac graphics. I dabble in some 3-D rendering and the software I use offers NVidia’s iRay renderer, which only supports CUDA for GPU acceleration. Yes, OpenCL has caught up with support for a lot of stuff, but there are still plenty of CUDA only options out there and this means that any such users are basically being told that Apple has no place for them. I have a late 2015 iMac 5K so I’m not thinking of replacing yet, but my aging MacBook Pro has no compelling upgrade path so I’m already being pulled in the Windows direction, the lack of a potential NVidia support down the road makes this an easier decision.
  • The fact that it’s not coming out until December this year tells me the upcoming modular Mac Pro is nowhere near ready and won’t be for some time. I know we were already told “not this year” but if the iMac Pro isn’t coming out until December then there’s no way the Mac Pro is coming out early 2018, I’m guessing later 2018 at the absolute earliest now.
  • The $5000 starting price for the iMac Pro worries me about what the Mac Pro will cost when it comes out.
  • There’s literally nothing of interest that’s come out now. The Macbook Pro got a very minor speed an graphics upgrade but is still limited to 16GB. Basically we’re being told to hold our breath for another 6 months while Apple gets their pro line back in order.
  • The external GPU offering also looks compelling, but again comes stock with an AMD GPU. When NVidia announced the new Titan XP earlier this year they also announced Mac driver support was coming, and did a week later. NVidia has stayed committed to the pro/enthusiast Mac customer, I was really hoping that this was an indication that things were swinging back in that direction with Apple too so I’m really disappointed to see zero official NVidia options at WWDC.
  • On a more positive note, at least Apple is starting to show us a few things on the pro side and seems to be getting that they need a bit more transparency there. At least we’re hearing that a new Mac Pro will be coming, we’re seeing an iMac Pro well in advance of it being available. I do like this trend overall, it’s just feeling a little too little too late.

MPG: these are all good points.

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