Tuesday, 26 December 2017

iMac Pro vs 27-inch iMac

Apple has the attention of the creative professional world right now with the launch of the new iMac Pro. However, there is another iMac that could answer their needs.

In this comparison we will ask the question, should you buy a new 27-inch iMac or the iMac Pro? (If you are wondering what the Mac Pro might offer when Apple introduces that new model, read our Mac Pro 2018 (or 2019) preview.)

Price - what you get for your money

The first thing to look at is the price. The iMac Pro has a high price attached to it, starting at around £4,899 inc VAT (or $4,999).

If that is too much money for you to consider paying for a new Mac you might as well stop reading and head to our review of the new 27in iMac for 2017.

You can buy a 27-inch iMac for £1,749/$1,799. However, if you were to spec up your iMac to the max, you could spend £4,949.

That top-spec 27-inch iMac includes a quad-core Intel i7 Kaby Lake processor running at 4.2GHz (or Turbo Boost of 4.5GHz), 64GB RAM, a 2TB SSD and the AMD Radeon Pro 580 graphics with 8GB video memory.

Is that build-to-order iMac comparable to the iMac Pro?

The standard configuration of iMac Pro comes with an eight-core Intel Xeon W CPU (configurable to 10, 14 or 18 cores), 32GB RAM (configurable to 64GB or 128GB), a and a 1TB SSD (configurable to 2TB or 4TB).

The eight-core (or more) workstation standard Intel Xeon W processor and the Radeon Pro Vega graphics card make the iMac Pro a far more powerful machine. But do you really require that much power? If you are editing 8K RED video, H.264 4K footage, or 50 Megapixel RAW stills perhaps you do. If you are just looking for a super fast Mac, even if you are a gamer, the iMac Pro is probably overkill for you.

Xeon versus i7 processor

How will the eight-core Intel Xeon W processor in the iMac Pro (which Apple said will offer Turbo Boost of up to 4.5GHz) compare to the 4.2GHz quad-core Intel i7 Kaby Lake processor offered as a build-to-order option for the iMac (also with Turbo Boost up to 4.5GHz)?

The biggest and most obvious difference is the number of cores. Even if the i7 processor had a faster clock speed than the Xeon chip, the fact that it has fewer cores would mean it would be slower.

Increasing the processor speed doesn’t bring as much performance improvement as an increased number of cores does. This is because more cores allow for more work to be performed at the same time.

The amount of cache is also noteworthy. This is the small amount of memory located directly on the processor. Core processors come with 8MB cache while Xeon CPUs top 60MB, although Apple says that the cache in the iMac Pro will max out at 42MB.

For many applications cache is another important contributor to performance. For example, if two processors have the same GHz, but different amounts of cache the one with more cache will perform better. So you can expect more from the Xeon in this case too.

Hyper-threading (HT) is another feature to take note of. Hyper-threading allows multiple tasks to be performed at the same time by the same core. Both the Core i7 and Xeon processors have hyper-threading enabled by default so you will be able to take advantage of it on both Macs.

Note though that the i5 processor in the other iMacs doesn’t include hyper-threading. This is a feature you only get with the i7 iMac build-to-order option.

Finally, the power dissipation of the Xeon is better than that of the Core i7. This means that the Xeon can overclock more easily, as long as it has the means to keep cool.

There are some key differences between the two processors, with the Xeon coming out on top. But the i7 is still a very good choice.

This doesn’t mean that the 4.2GHz quad-core Intel i7 Kaby Lake processor would slow you down, of for that matter the Intel i5 chip that comes as standard. It really depends on the nature of your work.

If you want to find out more about the different types of processor available in the Mac range read this: How to choose the Mac with the best processor for your needs.

Radeon Pro vs Vega Graphics

How will the AMD Radeon Pro 580 graphics with 8GB video memory compare to the Radeon Pro Vega graphics in the iMac Pro?

AMD says that Vega will deliver its biggest graphics improvements in five years and Apple says that the Radeon Pro Vega is “over three times faster than any previous iMac GPU”.

Apple is using the Radeon Pro Vega 56 in the Mac Pro. This GPU offers 8GB HBM2 memory - that’s high-bandwidth memory. There will also be a 16GB HBM2 memory option for the iMac Pro.

HBM2 memory is expected to be valuable to anyone working in virtual reality, so the new iMac Pro is ideal for that market.


Another factor in the iMac Pro’s favour is the inclusion of ECC memory - Error-Correcting Code memory.

ECC includes special circuitry for testing the accuracy of data as it passes in and out of memory so it can detect and correct any corruptions.

This kind of memory is suited to scientific or financial applications that cannot tolerate any data corruption.

There are some other significant differences. The Xeon chip in the iMac Pro will support more memory - Apple says up to 128GB, but there are some Xeon chips that support more than 1TB of memory.

As for the Core i7, the chip used in the iMac officially supports 64GB, although some Core i7 chips support 128GB RAM.

16GB of RAM is likely to be sufficient for the vast majority of Mac users though.

Should you wish to update the RAM at a later date it may be easier for you do do so it you own a 27-inch iMac which has easily accessible RAM slots behind the screen.

There is no easy-access door on the back of the iMac Pro granting access to the RAM. We"ve heard that the RAM modules in the iMac Pro are larger, so Apple has had to relocate the memory modules with the result being they are less accessible. Apple says the memory is not a user-upgradable, however, it seems that a specialist would be able to perform the upgrade for you.


The new iMac Pro will offer a 1TB SSD as standard, but Apple says it will offer up to 4TB SSD.

The top of the range build-to-order iMac offers a 2TB SSD.

Since we are comparing the build-to-order iMac with the standard iMac Pro, in this case you would get more storage for your money if you bought the non Pro iMac.

That 2TB SST costs you a whopping £1,260/$1,400, so you could shave off more than £1,000 of the price of your build to order iMac, which would cost ‘just’ £3,689.


The 27-inch screen on the iMac Pro will offer the same 5,120x2,880 resolution 5K Retina display, with the same 500 nits of brightness, 14.7 million pixels, P3 colour gamut and support for over a billion colours, as the standard 27-inch iMac.

There is no reason in terms of display to choose the iMac Pro over the standard 27-inch iMac.


While the standard 27-inch iMac offers two Thunderbolt 3/USB Type-C ports, the iMac Pro offers four Thunderbolt 3/USB Type-C ports.

This means you could connect two additional 5K monitors to your iMac Pro for a whopping 44 million pixels, and hook up two high-performance RAID arrays and enjoy 40Gb/s transfer speeds.

One other thing the iMac Pro offers that the standard iMac doesn"t is 10Gb Ethernet.

The standard iMac offers a 1Gb Ethernet socket. This means that sharing files on the iMac Pro, or working with high-performance network storage, will be up to 10 times faster.

It also includes an SDXD card slot that supports UHS-II (that"s Ultra High Speed) for even faster data transfer rates.


The most obvious design difference between the two machines is the Space Grey case of the iMac Pro, which gets a brand new space grey Magic Keyboard to match the new look.

The real design changes are on the inside. Apple has had to completely rethink the thermal architecture of the iMac in order to house the new components inside the Pro. You are unlikely to see any evidence of this other than the fact that there are two fans inside the iMac Pro and a pair of horizontal vents across the bottom of that machine, while a regular iMac has a single fan plus one vent.

You can also read our comparison of all the "pro" Macs here, find out which is the best Mac for pros.

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