Andrew Cunningham

Lee Hutchinson

Lee Hutchinson

Lee Hutchinson

A couple of weeks back, we took a look at the new 21.5-inch 4K iMac. It’s a solid desktop with a great screen, though its default configuration leaves something to be desired (particularly its slow 5400RPM hard drive).

If you really ask a lot of your computing equipment, though, there’s still no substitute for the 27-inch 5K version. More divides the small and large iMacs than ever before: the 27-inch versions include new Skylake processors from Intel, while the 21-inch versions use the older Broadwell architecture. You can only get dedicated GPUs in the 5K iMacs. The Mac Pro is still Apple’s fastest Mac if your workloads routinely max out multiple CPU cores and GPUs, but for other power users and pros the 27-inch iMac is the one to get.

The outside

We’re going to keep this really, really short, because very little has changed about the exterior of the 5K iMac. Even some of the internal upgrades that were new to the 21.5-inch models—Thunderbolt 2, for one—were already included in the 27-inch model last year.

Specs at a glance: 27-inch 2015 5K iMac Screen 5120×2880 27" IPS display (217 ppi) OS Mac OS X 10.11.1 CPU 4.0GHz Intel Core i7-6700K (Turbo Boost 4.2GHz) RAM 32GB 1867MHz DDR3 GPU AMD Radeon R9 M395X with 4GB GDDR4 RAM Storage 1TB NVMe SSD, four PCIe 2.0 lanes Networking 1.3Gbps 802.11ac, Bluetooth 4.0, gigabit Ethernet Ports 4x USB 3.0, 2x Thunderbolt 2, headphone jack, SD card slot Size 20.3 x 25.6 x 8 inches (51.6 x 65.0 x 20.3 cm) Weight 21 lbs (9.54 kg) Starting price $1,799 As reviewed $4,099 Other perks FaceTime HD camera, dual noise-canceling mics, ambient light sensor, Kensington lock slot

One improvement is a wider color gamut, the same one we saw in the 4K iMac. Previous iMacs used the sRGB color space, but the new Retina models support "over 99 percent" of the DCI-P3 color space common in digital movie theaters. DCI-P3 encompasses the entire sRGB color space but is capable of displaying more shades of red and green (which also affects secondary and tertiary colors like yellow, orange, magenta, and cyan, though blues in DCI-P3 are roughly the same as in sRGB).

To support this wider color gamut, Apple has switched away from using standard white LEDs for backlighting, which typically combine a blue LED with a yellow phosphor to create white. Apple is now using red-green phosphor LEDs to expand the color gamut, a strategy previously demonstrated by LCD makers like Sharp.

Also new are the input devices, the Magic Keyboard, Magic Mouse 2, and Magic Trackpad 2. All three replace AA batteries with rechargeable li-ion versions. The mouse looks pretty much the same, but the keyboard and trackpad are both slimmed down and streamlined.

Lightning cables are used to recharge the accessories, but they'll also carry data when connected to your Mac. This obviates the need for separate wired and wireless versions, since any wireless accessory effectively becomes a wired accessory when you plug it in (that said, the placement of the Lightning port on the bottom of the Magic Mouse 2 makes this impractical). When you plug in the accessories to a Mac running El Capitan, they’ll also automatically pair with it.

The keyboard and mouse are included with all iMacs for no additional charge, but the trackpad will cost $50 extra.

The inside

Here’s where we get to the fun stuff. The new iMacs jump two CPU generations, one GPU generation, and double the amount of storage bandwidth that the old ones had.

Apple sent us the fastest version of the 27-inch iMac that it makes, complete with 32GB of RAM and a 1TB SSD—this computer retails for an eye-popping $4,099, though a full $1,300 of that is wrapped up in storage and memory upgrades. It’s pricey, but boy is it fast.

The CPU is a Core i7-6700K, a 4.0GHz (4.2GHz Turbo) high-end, quad-core Skylake CPU that we’ve actually already reviewed. Intel’s year-over-year CPU performance gains have slowed in recent years, so if you’ve already got a similarly clocked Haswell chip the gains are relatively small. If you’re replacing a quad-core iMac from 2010 or 2011, you can expect to see some more significant boosts. We pulled results for half a decade of high-end iMacs (plus the fastest 4K iMac with Broadwell) from the Geekbench results database to illustrate.









This iMac also widens the performance gap between it and the quad-core version of the Mac Pro—with the 6700K, it’s the undisputed single-core performance champion, the fastest processor you can get in any Mac in the entire lineup. Multithreaded tasks still do better with more cores, though, so if you want 6, 8, or 12 CPU cores, the Mac Pro is still the only way to go. The 5K iMac actually stands up fairly well to the 6-core Mac Pro, but the 8- and 12-core versions still blow it away. If Apple ever gets around to updating its pro desktop again, Intel even has single-socket Xeon CPUs with 14, 16, and 18 cores now.

Listing image by Andrew Cunningham