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While the all-in-one desktop model from Apple that has undergone the biggest change this year is the 21.5-inch iMac, moving up to a 4K display , the 27-inch line also has some notable late-2015 updates.
The two biggest changes are that every 27-inch iMac now includes Apple's 5,120x2,880-pixel-resolution Retina Display, and the entire 27-inch line has been moved up to Intel's latest sixth-generation Core i-series processors, also known by the code name Skylake. These iMacs were previously two generations of CPU behind.
Beyond that, it's little surprise that the new Apple iMacs all look the same as models from the past several years. The basic design language of the iMac has changed little since 2012, when it adopted the current setup of a slim, bowed screen sitting on top of an aluminum stand and minimalist base, a look that still manages to feel fresh years later.
Having tested and reviewed the first appearance of this 5K display in late 2014 , we can say that in person, the 5,120x2,880 display is simply stunning, especially when displaying high-res full-screen photos and video. The previous non-5K versions had a 2,560x,1440 display, making this 2x jump especially impressive.
During that 5K initial testing, we said: "No matter how close we got, no pixels were visible on the 5K Retina Display. From our hands-on, and eyes-on, testing, it's clear that there is a measurable difference between the 5K Retina Display, and the 2,560x1,440 dis`play on the previous non-5K model."
Also new for 2015 are updated AMD graphics cards. Previous 27-inch iMacs, even the 5K models, used the AMD R9 290X or 295X. Now, the default is the newer AMD Radeon M380, with the faster M390 and M395 as upgradable options. Also option, Fusion drives for faster storage, which is Apple's term for hybrid hard drives combining a standard spinning hard drive with a smaller amount of flash storage.
Besides the higher screen resolution and new CPUs, the biggest obvious change to the iMac line is the revamped collection of accessories bundled with it. The wireless Apple Keyboard, Magic Mouse and Magic Trackpad -- all familiar sights on Apple users' desks around the world -- have gotten their first overhaul in years.
All three lose their reliance on disposable batteries, instead moving to internal rechargeable lithium on batteries. That allows the keyboard and trackpad to slim down, removing the rounded battery compartments that dominated the previous designs. The Magic Keyboard is smaller and flatter, but has slightly larger key faces. The Magic Trackpad 2 has a larger surface area -- it looks huge compared with the original version -- and now supports Force Touch, just like the pads in the MacBook and MacBook Pro. The Magic Mouse 2 looks the same, but is a hair lighter with better rubber tracks along the bottom.
As one might expect, a 27-inch iMac with the latest Intel processors, discrete AMD graphics, at least 1TB of storage and a 5K-resolution display requires a hefty investment. The late-2015 27-inch iMac starts at $1,799, with upgraded base configurations at $1,999 and $2,299 (£1,449, £1,599 and £1,849 in the UK; AU$2,799, AU$3,099 and AU$3,599 in Australia).