27" iMac full review

The 2015 27in 5K iMacs jump from Haswell to Skylake - which is two CPU generations, they also move up one GPU generation, and the storage bandwidth is twice as much. In addition, the display quality is better than ever and you can buy 64GB of third-party RAM as a user upgrade. All this adds up to a pretty impressive update. Our main criticism is that the Fusion Drive isn’t standard across the range, and, even worse, the SSD part is now much smaller. However, the new 27-inch iMac line-up is great value for money, if you were to purchase a 5K display of this quality it would cost a lot more than the price of the 5K iMac, and it wouldn’t come with a fast, capable, fully functioning computer

 There are three standard 27in models. These are spec-ed and priced as follows:

iMac, 27in, quad-core 3.2GHz, 1TB hard drive, AMD Radeon R9 M380, £1,449

iMac, 27in, quad-core 3.2GHz, 1TB fusion drive, AMD Radeon R9 M390, £1,599

iMac, 27in, quad-core 3.3GHz, 2TB fusion drive, AMD Radeon R9 M395, £1,849

If you were to fully spec out the ultimate top of the range build-to-order (BTO) model you could get: 4GHz quad-core i7, 32GB of RAM, a 1TB SSD, and faster AMD Radeon R9 M395X graphics – it would cost you £3,289. £1,440 more than the standard top of the range model, and just £10 less than the top of the range standard Mac Pro, which costs £3,299.

There’s also a new range of 21.5in iMacs, including one with a 4K Retina display, which we look at here: New 21.5-inch iMac with Retina 4K display. Read more about the new range of iMacs here: Apple launches 21.5in Retina iMac, updates 27in iMacs with Skylake.

Update: While the prices in this review were accurate at the time of writing, Apple has since raised the price of the entire Mac range in the UK, with some Mac prices being raised by as much as £500. For reference, we've decided to keep the original prices in the review, but you can find updated pricing below and more information on the price hike here: Apple price increases UK

iMac, 27in, quad-core 3.2GHz, 1TB hard drive, AMD Radeon R9 M380, £1,749

iMac, 27in, quad-core 3.2GHz, 1TB fusion drive, AMD Radeon R9 M390, £1,949

iMac, 27in, quad-core 3.3GHz, 2TB fusion drive, AMD Radeon R9 M395, £2,249

2015 27in iMac with Retina display: Processors and speed tests

All the new 27in models include Skylake quad-core i5 processors from Intel running at 3.2GHz or 3.3GHz. Skylake is the name of Intel’s sixth generation processors. Intel claims that these processors offer better CPU and GPU performance while reducing power consumption. They use the 14nm manufacturing process (which is the same as Broadwell).

Skylake launched very soon after Broadwell did – mostly because Broadwell encountered many delays. As a result many manufacturers have side stepped Broadwell all together. Note: The 21in iMac models are using the older Intel Broadwell chips because Apple relies on the on system graphics chip for those models and as yet that isn’t available for Skylake.

On the entry-level model the Skylake processor is a marked leap up from the 3.2GHz processor in the original entry-level model. However, the mid-range model sports the same 3.2GHz processor (the difference between these two models is in terms of graphics and storage, more on that below).

This might appear to indicate a decline on the speed of the previous mid-range model, which offered 3.3GHz for the same price. However, it should be noted that these are next generation processors so theoretically the 3.2GHz Skylake chip of this generation could be faster than the 3.3GHz chip from earlier in 2015.

Similarly, at the top of the late 2015 iMac range is a 3.3GHz processor, again a slower clock speed than the older model.

Testing suggests that if you happen to have a Mac with a a similarly clocked Haswell chip, the gains are quite small, although when it comes to the entry-level model, the £1,449 27in iMac with its 3.2GHz Intel Core i5-6500 seems to clock in at about 10% faster than the 3.5GHz Core i5 Broadwell chip in the original 5K iMac model from 2013.

There's also a BTO model that offers a quad-core Skylake i7-6700K, running at 4.0GHz (or up to 4.2GHz Turbo). This processor in the BTO iMac is also faster than the processor in the entry-level quad-core Mac Pro (which costs £2,499). That doesn’t mean the 5K iMac is necessarily a better choice than the Mac Pro, which also offers far faster 6, 8, or 12 CPU cores, which might be what you need.  The 8- and 12-core versions of the Mac Pro are in a different league to the iMac, imagine what’s possible if Apple finally upgrades the two year old Mac Pro.

We haven’t run Geekbench on the new 27in 5K iMacs yet, but we have these results from the models we tested this summer that we will add here now in preparation for the new set of results.

The results were as follows:

Geekbench 3 single-core 64 bit

3.3GHz 27in 5K iMac (mid 2015) : 3,691

Geekbench 3 multi-core 64 bit

3.3GHz 27in 5K iMac (mid 2015) : 11,769

2015 27in iMac with Retina display: Graphics and speed tests

The new 27in iMacs features AMD Radeon R9 GPUs, with each model getting a more advanced graphic chip.

The entry-level 3.2GHz model features the AMD Radeon R9 M380 with 2GB video memory

The mid-range 3.2GHz model features the AMD Radeon R9 M380 with 2GB video memory

The top-of-the-range 3.3GHz model features the AMD Radeon R9 M395 with 2GB video memory
with 2GB video memory

BTO iMac offers a AMD Radeon R9 M395X with 4GB video memory

One of the key differences between the 21.5in and the 27in iMac is that the larger model offers a dedicated GPU while the 21.5in models offer a graphics chip integrated on the processor itself. The graphics processors in the newest 27in iMac are all from AMD, and you will find the Radeon R9 M380, R9 M390 and R9 M395X depending on which model you buy.

It appears that despite the upgrade, these AMD GPUs aren’t a lot better than the graphics chips in the previous models. However, at the top end the new GPU is said to be better than the GPU in the previous 27 iMac which gamers complained would overheat and lower its clock speed. As a result, the AMD Radeon R9 M395 GPU in the £1,849 5K iMac is able to handle some mainstream games at decent settings, but if you are a keen gamer, you will be disappointed, it won’t be capable of the same performance as a gaming PC.

Using the Unigine’s Heaven benchmark we can get some idea of the 2015 iMacs’s gaming capabilities. Having set the resolution to 2,560 x 1,440 with medium detail we found that the R9 M390 (the £1,599 model) was able to manage 26fps. So if you do want to use your iMac for gaming, its best to opt for about 2,560 x 1,440 resolution for the least stuttery experience. It seems that the 14.7 million pixels the iMac is capable of are just too many for it to cope with when dealing with high graphics gaming. If you need to max out multiple CPU cores and GPUs then the Mac Pro is the machine for you.

The 21in models have the graphics chips integrated on the CPU, so if you need the extra power of a discrete graphics processor you will be better off opting for the 27in models. The new 21.5in iMacs can’t even compete with the older 27in iMacs in terms of graphics. Which isn’t a big surprise given the fact that the GPU is integrated on the processor in the 21in models and separate in the 27in iMacs. Our colleagues at Macworld US ran Cinebench tests and found that while the new 3.1GHz 21.5in iMac performed better than it’s predecessor, despite the fact that it is driving four times more pixels, it was left behind by the 5K 3.3GHz iMac that launched in mid 2015.

2015 27in iMac with Retina display: Display

Unlike the 21in iMac range, where only the top of the range model gains a 4K Retina display, Apple’s range of 27in iMacs are all now furnished with a 5K Retina display. Prior to the October range update only two of the 27in iMacs had the higher resolution display.

All three Macs offer a resolution of 5120 x 2880 - that’s 67 percent more pixels than a 4K display.

The new 27in iMac has a display that might sound the same on paper to the 5K display in the preceding models, but it actually has a wider colour gamut. The newer models have a wider P3 colour gamut and will deliver  25 percent more colours than the previous one, according to Apple. It is capable of displaying 130 percent of the sRGB gamut, according to tests.

That original 5K display was found to have a full 100 percent coverage of the basic sRGB colour gamut. In terms of the Adobe RGB colour space, that iMac recorded 78 percent cover, althoguh others have seen it achieve 86.1%. These new 27in Retina models are also able to show more than 99 percent of the DCI-P3 colour space. DCI-P3 is the colour space for digital movie projection. It encompasses the entire sRGB colour space and in addition can display even more shades of red and green (the knock on effect of which is that colours like yellow, orange, and magenta also improved). Only blues and cyan are lacking - or rather pretty much the same as they are in sRGB.
In order to widen the colour gamut Apple switched away from using white LEDs for backlighting (actually a white LED is a combination of a blue LED with yellow phosphor). Instead Apple is now using red-green phosphor LEDs.

Moving on to resolution, that hasn’t changed, the 27in iMac still offers 5,120 x 2,880 resolution which adds up to 14.7 million pixels. When we tested the 5K Retina display on the 2014 5K Retina iMac we saw it turn in some of the best numbers our colorimeter had ever measured. On this model, the contrast ratio is 1,166:1, with regards to the previous generation, at its full output we saw the highest contrast ratio we’ve measured in the standard chequerboard test, returning a figure of 1160:1. In evaluation the new Delta E rating was 0.72, while previously in our colour accuracy test of the 2014 top of the range Retina model, returned an average of 1.66 Delta E (A Delta E of 1.0 is considered the smallest color difference the human eye can see).

When we tested the original 27in Retina iMac we also found full brightness to be 445 cd/m^2. In some tests the new 27in iMac managed 382 cd/m^2 according to a light meter, which is an impressive number although not quite as bright as the older model, although other tests have found the new monitor managed 466cd/m² (perhaps there is a difference in screen supplier).

One criticism of the new 27in iMac displays is that the iMac’s backlighting doesn't appear to be quite as rigorous as it is on some pro monitors, in testing, it was found to be between 10% and 16% dimmer in the bottom-left corner, obviously designers want a display that is consistent across the whole panel. (The 21in model didn't suffer this fault, so again, it could be a faulty batch).

The other along standing criticism is that there’s no height adjustability – you can only tilt the iMac back and forth, the only way to raise the monitor is to sit it on one of those hard back books you have lying around.
The other criticism is that Apple you can’t use Target Display mode on the 27-inch iMac so you can’t plug it in to another computer (not even a Mac Pro) and use it as a 5K monitor. We hope that Thunderbolt 3 makes it into the next generation as this could allow this.

With all that said, there are not many 5K monitors that you can buy right now, and certainly not any that cost around £1,500 and come with an integrated computer.

There is more to the Retina display than being able to see subtle details thanks to the extra pixels. The high pixel count means you can set the display to an alternate resolutions without sacrificing image quality. For example, if you want everything to be a little bit bigger you can set the 5K iMac to emulate a smaller monitor (via System Preferences > Display).

Read our Mac buying guide

2015 27in iMac with Retina display: Ports

The ports haven’t changed on the mid-range and top-of-the-range 27in iMac (although the entry-level previouls non-Retina 27in iMac and the 21in iMac range was so out of date that Apple had to sort out some of the embarrassing ommissions in that model, such as Thunderbolt 2 - those models only offered Thunderbolt 1). Speaking of which, we’d like to see Thunderbolt 3 in the iMac, as we said in the display section, Thunderbolt 3 would allow users to plug the iMac into another computer and use that 5K display, it would also bring USB Type-C (which is incorporated in Thunderbolt 3) and obviously it would speed up any accessories plugged in to those already pretty speedy ports.

Right now the 27in iMac will give you two Thunderbolt 2 ports, four USB 3.0 ports, an SDXC card slot, a headphone jack and an Ethernet port

You’ll also get some not-so-bad integrated speakers, along with the new Magic Keyboard and Magic Mouse - unless you’d prefer to opt for the Magic Trackpad. The new 27in iMacs ship as standard with the new Magic Mouse 2 (or you can switch it to the Wired Apple Mouse if you prefer).

The new Magic Trackpad 2 costs an additional £44 as a build to order option, or you can get both the Magic Mouse 2 and the Magic Trackpad 2 for £109. In this case you are essentially paying for the Magic Trackpad 2; if you were to buy them separately the new Magic Mouse 2 costs £65 and the Magic Trackpad 2 costs £109 - the mouse is bundled with the iMac so you don’t have to pay for it in this instance.

You can purchase the Magic Mouse 2 on the Apple Store here, and the Trackpad 2 is available from the Apple Store here. There's also a new Magic Keyboard (Apple's getting a bit carried away with the Magic). The Magic Keyboard is available to buy here.

Find out what port does what here: Guide to Mac and iPhone ports: what is USB Type-C, Thunderbolt & Lightning

2015 27in iMac with Retina display: Storage

The storage is one area where the iMac is let down - particularly at the 21.5in level, but also on the entry level 27in Retina model. Apple still uses an old fashioned hard drive (HDD) in these models as standard. The 21.5in models are even worse off, those hard drives are even slower than the one the 27in model - 5400rpm compared to 7200rpm. The other two 27in Retina iMacs ship with Fusion Drives as standard which is a blessing at least because it offers the best of both worlds, a fast flash (SSD) drive and a large HDD in one. Opting for a hard drive if you are used to flash storage will make the Mac feel slow.

The Fusion Drive combines a large hard drive for space, and a smaller SSD for quick access of frequently used files and start up information. The way the Fusion Drive works is it will store the important OS X files and applications that you use the most frequently, so that these load up quickly, and as a result you can get near instantaneous wake from sleep. There also used to be plenty of space to store frequently accessed files on the SSD but the bad news for this generation is that Apple has slimmed the SSD part of the 1TB Fusion Drive down to a measly 24GB of storage from 128GB. As a result it’s cheaper as a build to order option (£80), but frankly it limits the storage so you won’t be able to store as many frequently used large apps and files on the SSD, which could spell a slower experience day to day. The 2TB (an extra £160, or standard on the top-of-the-range model) and 3TB (an extra £240) versions of the Fusion Drive still offer the 128GB flash drive.

Now that Apple has reduced the spec of the Fusion Drive and reduced the build-to-order price, we think all iMacs should ship with a Fusion Drive, surely Apple can swallow the price of what we think is an essential £80 update. For now we strongly recommend that you upgrade to Fusion, or if you don't need the space, grab a SSD at the build to order stage when you purchase the machine as it will make a significant difference the the speed at which it runs.

Speaking of SSDs, back in 2013 Apple switched from the SATA interface to PCI Express which improved performance no end (PC manufacturers still haven’t done this). Going one better, this year Apple has further improved performance by attributing even more PCI Express bandwidth to its SSDs. The SSD and Fusion Drives in the new iMacs now get four PCI Express 2.0 lanes which is double that of the 2013 and 2014 iMacs. The new drives also use the NVMe protocol. Because the flash storage can take advantage of upgraded storage controllers and four lanes of PCI, Apple says this allows them to achieve flash-storage transfer speeds up to 2.5 times those of previous models.

If you don’t need the space but would love things to be as fast as possible, and you will be frequently accessing large media files, the Flash Storage options might be preferable. For the £1,449 iMac, there’s a 256GB Flash upgrade for £80 or 512GB for £320. These prices are lower for the 27in models than the 21in models). On the £1,599 model 256GB Flash is £80, 512GB is £320, and 1TB is a wallet-wrecking £720.

As you’d expect, with a Fusion Drive you can access files pretty quickly, for example, in tests we saw 687MB/sec for reading files, and 170MB/sec for writing them to the disk. This isn’t as fast as pure flash storage though.
It’s our opinion that no iMacs should be using hard drives in this day and age. If you are desperate for the extra capacity of a HDD, get a separate hard drive, or even better a NAS drive.

If you are thinking of getting the entry-level 27 Retina iMac you might think that £80 is a small price to pay for the benefit of the Fusion Drive, but it will bring the price of the iMac to £1,529, so you might as well skip this model and buy the £1,599 iMac which comes with the Fusion Drive as standard. You’ll also get the slightly better graphics card. It depends if you think that the £70 difference is enough to warrant the improved graphics. Our advice if you are buying the entry-level model, avoid the hard drive, if you really need all that storage get an external drive and use that.

Find out more about which storage to add to your Mac here: How to add more storage to your Mac | Hard drives, flash storage, NAS - find out which storage option is best for you and SSD vs hard drives: which is the best storage to have in a Mac

2015 27in iMac with Retina display: RAM

Macs are notoriously difficult to upgrade, in fact the 21.5in iMac is impossible to upgrade yourself so we recommend making sure you get all the extras you might need at point of purchase. However, there is a little more flexibility with the 27in model. While the new 27in iMacs comes with 8GB RAM all models are configurable to 32GB at point of sale.

You can opt for up to 32GB of RAM at point of purchase, but you can also access the RAM slots later on and there is an option to buy 64GB of RAM from a third party and add it yourself at a later date. If you are unlikely to tinker with your iMac or needs that much RAM, we recommend that you purchase the 16GB RAM option at the build to order stage - it’s an extra £160 but we think it will be worth it in the long run.

Incidentally, if you purchase 32GB RAM as an upgrade from Apple it will cost an extra £480. You will be able to purchase 64GB RAM from OWC for $1195 (approx £772, UK price TBC). German reseller Memphis has been in touch to confirm that they will be selling 64GB RAM for the new iMac on Amazon UK - you can buy the 64GB RAM-Kit here for £575. We also expect that Crucial will be offering 64GB RAM as well.

2015 27in iMac with Retina display: Price

in mid 2015 Apple reduced the price of the top of the range iMac from £1,999 to £1849. If you were hoping the company might have reduced prices further you’re out of luck, but at least the new entry-level 27in iMac retails at £1,449 (the same price as it’s non-Retina predecessor), meaning you can now get a 5K Retina iMac for less than £1,500. Mind you, can now purchase a Retina iMac for £1,199 albeit with a 21in display. But it does mean the point of entry for a Retina display iMac is lower than ever.

The full range of 27in iMacs are priced as follows:

iMac, 27in, 3.2GHz, 1TB hard drive, AMD Radeon R9 M380, £1,449

iMac, 27in, 3.2GHz, 1TB fusion drive, AMD Radeon R9 M390, £1,599

iMac, 27in, 3.3GHz, 2TB fusion drive, AMD Radeon R9 M395, £1,849

You can buy the new 27in Retina iMac from Apple’s online store here.

You can buy the new 21in Retina iMac from Apple's online store here.

As we discuss in our review of the 21in Retina iMac, which even at £1,199 is not the cheapest Mac with a Retina display you can buy, you can get a 13-inch Retina MacBook Pro for £999 – that’s a lot less than the entry price for the 27in Retina iMac, but that MacBook has a far smaller display and a slower processor, so if you will benefit from the larger display you may feel that the extra £450 is worth it – after all, were you to fork out for a 5K display to use with your laptop you’d probably be looking at spending a lot more. Read more Retina MacBook Pro reviews here.

Interested in the earlier iMac models? There are likely to be some discounts on earlier models available from Apple’s refurbished store (although right now we can’t see any). You can read more iMac reviews here.

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