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Apple 21.5-inch iMac with Retina 4K Display (2015) review: Display dazzles, but options are fewer

  • Editors' rating
    8.0 Excellent
  • $819.99


  • Bright, colourful 4K display
  • Broadwell update provides strong processor performance
  • Slimline, all-in-one design


  • Slow hard drive
  • No longer includes discrete GPU
  • Limited upgrade options

The 27-inch version of the iMac has received a number of major updates in the last year or so -- most notably, of course, the introduction of the Retina 5K Display that effectively repositioned the larger iMac as a workstation for professional graphics and video-editing.

In contrast, the 21-inch version of the iMac has largely been ignored in recent years, and although its elegant design has found a home in many reception areas and executive desks (often as a kind of corporate fashion statement), its relatively modest specification has left it looking overpriced compared to desktop systems from rival PC manufacturers. This 2015 update is therefore long overdue, and the top-of-the-range model reviewed here introduces a number of long-awaited improvements.

Three's company

As always, the 2015 edition of the 21.5-inch iMac is available with three standard configurations. The prices for all three models remain unchanged, with the 'affordable' model that Apple launched last year still costing £899 (inc. VAT, or £749.17 ex. VAT) and retaining its predecessor's 1,920 by 1,080 resolution. However, that model receives only a modest update and its 1.6GHz dual-core Intel Broadwell Core i5 processor means that it offers only entry-level performance at a mid-range price.


The 21-inch 4K iMac is joined by the recently updated 27-inch model with a 5K display.

Image: Apple

If you do require stronger performance then there's a model with a quad-core Broadwell processor running at 2.8GHz, although that rises in price to £1,049 (inc. VAT, or £874.17 ex. VAT) and still only offers 1,920 by 1, 080 resolution. Both models are considerably more expensive than PCs with similar specifications, and Apple seems to be relying on the iMac's striking slimline design to justify its high pricing. That's very much in contrast to the genuinely aggressive pricing of the iMac's 27-inch counterpart, with its outstanding 5K display and discrete graphics card.


Apple's Magic Keyboard, optional Magic Trackpad (with Force Touch) and Magic Mouse have all been updated.

Image: Apple

Apple has also updated its wireless Magic Mouse and Magic Keyboard, which now both include rechargeable batteries. The keyboard has also been redesigned, and provides a firmer, more comfortable feel when typing. However, its lack of numeric keypad and limited set of function keys means that it still doesn't really feel suitable for intensive, high-speed typing or number-crunching. There's a new version of Apple's Magic Trackpad available too, which is now larger and includes the pressure-sensitive ForceTouch feature that was recently introduced on the latest MacBook laptops. It's an attractive alternative to a conventional mouse, but is only available as an optional extra costing an additional £44 (inc. VAT, or £36.66 ex. VAT).

4K display

Those first two iMac updates are little more than speedbumps but, thankfully, the top-of-the-range model reviewed here does gain a more significant update in the form of the long-awaited Retina display. Again, the price remains the same, at £1,199 (inc. VAT, or £999.17 ex. VAT), but the display of this model now steps up from 1,920 by 1,080 to a full 4K display with 4,096 by 2,304 resolution. The image quality is certainly striking: not only is it sharper and more detailed than its predecessor, the image is also noticeably brighter and more colourful too. The scaling technology built into the Mac operating system also works well, ensuring that text, icons and other graphic elements remain clear and legible even at that high resolution.


The top-end 3.1GHz 21.5-inch iMac is the only model with a Retina 4K display with 4,096 x 2,304 resolution and DCI-P3 colour space support.

Image: Apple

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The 4K Retina display also supports the same DCI-P3 colour space as its 5K counterpart, which allows it to reproduce the full range of colours that can be captured by the latest professional dSLR cameras and video-cameras (while the two less expensive 21-inch models continue to use the more conventional sRGB colour-space). That will certainly appeal to users who need to do high-end photo- or video-editing, although professional users in those fields are more likely to opt for the larger 5K display and stronger performance provided the 27-inch model.


The higher resolution of the 4K display requires a considerable amount of horsepower to drive it, so the 21.5-inch iMac with Retina 4K Display incorporates a quad-core Broadwell i5 processor running at a healthy 3.1GHz, along with 8GB of RAM, which has been also updated to run at 1,867MHz. However, it's disappointing to note that this 'top-of-the-range' model is only equipped with an ageing 5,400rpm hard drive with 1TB of storage capacity. It also abandons the discrete nVidia GT 750M graphics card of its predecessor and now relies on the Broadwell processor's integrated Iris Pro 6200 GPU.

To be fair, the Broadwell processor performs very well, with a Geekbench 3 score of 12,750 for multi-core performance that ranks right alongside its high-end 27-inch counterpart. However, the reliance on integrated graphics means that the 21.5-inch iMac with Retina 4K Display manages a relatively modest 48fps for OpenGL performance when running the Cinebench R15 test suite, which is just 49 percent of the score achieved by the recently updated 27-inch iMac.

The build-to-order upgrade options for this model are also quite limited -- presumably to encourage power-hungry users to opt for the more expensive 27-inch model. There's no longer any option to add a discrete graphics card at all and, of course, no expansion slots within that slimline chassis that would allow users to upgrade the iMac themselves. There's just a single processor upgrade available, with a 3.3GHz model costing an additional £160 (inc. VAT, or £133.33 ex. VAT). Thankfully, though, Apple has at long last reduced the price of its storage upgrades, with a hybrid Fusion drive -- which adds 120GB of solid-state storage to enhance performance -- costing just another £80 (inc. VAT, or £66.66 ex. VAT).


It's certainly not flawless -- Apple's short-sighted cost-cutting with storage and graphics components is a perpetual weakness -- but Apple's decision to keep the price unchanged means that the 21.5-inch iMac with Retina 4K display does provide considerably better value for money than its predecessor. Admittedly, the 4K display might be something of a luxury for business users who simply want to run Microsoft Office, but its impressive image quality and the strong performance of the Broadwell processor mean that the 21.5-inch iMac with Retina 4K Display will be an attractive option for users who need a fast and versatile desktop computer.


Type Personal computer
Product Form Factor All-in-one
Packaged Quantity 1
Built-in Devices 2 microphones, stereo speakers
Processor / Chipset
CPU Intel Core i5 (5th Gen)
Max Turbo Speed 3.6 GHz
Number of Cores Quad-Core
Processor Main Features Intel Turbo Boost Technology 2
Interface Type Serial ATA-300
Memory Speed 1867 MHz
Technology LPDDR3 SDRAM
Installed Size 8 GB
Environmental Parameters
Humidity Range Operating 5 - 95% (non-condensing)
Min Operating Temperature 50 °F
Max Operating Temperature 95 °F
Widescreen Display Yes
Monitor Features LED-backlit
Type LED
TFT Technology IPS
Diagonal Size (metric) 54.6 cm
Display Resolution Abbreviation 4K
Hard Drive
Interface Type SATA 3Gb/s
Spindle Speed 5400 rpm
Type HDD
Interface Class Serial ATA
Installed Qty 1
Capacity 1 TB
Type keyboard, mouse
Localization & Layout English
Hard Drive (3rd)
Type none
Wireless Protocol 802.11a/b/g/n/ac, Bluetooth 4.0
Optical Storage
Drive Type no optical drive
Type none
Installed Qty 1
Max Supported Qty 1
Type Core i5
Generation 5
Manufacturer Intel
Clock Speed 3.1 GHz
Card Reader
Type card reader
Supported Flash Memory Cards SD Memory Card, SDHC Memory Card, SDXC Memory Card
Storage Removable
Type none
Brand Apple
Product Line Apple iMac
Model with Retina 4K display
Localization English
Country Kits United States
Packaged Quantity 1
Compatibility Mac
Data Link Protocol Bluetooth 4.0, Ethernet, Fast Ethernet, Gigabit Ethernet, IEEE 802.11a, IEEE 802.11ac, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n
Compliant Standards Bluetooth 4.0, IEEE 802.11a, IEEE 802.11ac, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n
Wireless LAN Supported Yes
Monitor Type LED - IPS
Native Resolution 4096 x 2304 (4K)
Diagonal Size 21.5 in
Security Slot Type Kensington security slot
Type personal computer
Hard Drive Capacity 1 TB
Introduced Late 2015
Form Factor all-in-one
Manufacturer Form Factor all-in-one
Built-in Devices 2 microphones, stereo speakers
Graphics Controller
Graphics Processor Intel Iris Pro Graphics 6200
Dimensions & Weight
Width 20.8 in
Depth 6.9 in
Height 17.7 in
Manufacturer Warranty
Type 1 year warranty
Audio Output
Sound Output Mode stereo
Keyboard Name Apple Magic Keyboard
Connectivity wireless
Interface Bluetooth
Type none
Environmental Standards
ENERGY STAR Certified Yes
Mouse Name Apple Magic Mouse 2
Connectivity wireless
Technology laser
Interface Bluetooth
Features Multi-Touch
Physical Characteristics
Form Factor all-in-one
Weight 12.52 lbs
Type power supply
Min Operating Temperature 50 °F
Max Operating Temperature 95 °F
Operating System / Software
OS Provided: Type Apple macOS 10.13 High Sierra
OS Provided Apple macOS High Sierra 10.13
Type App Store, Apple AirDrop, Apple AirPlay, Apple Dashboard, Apple FaceTime, Apple GarageBand, Apple Keynote, Apple Mac OS X Mail, Apple Mission Control, Apple Numbers, Apple Pages, Apple Preview, Apple Safari, Apple Spotlight, Apple Time Machine, Apple iBooks, Apple iMovie, Apple iPhoto, Apple iTunes, Calendar, Contacts, Dictation, Facebook, Family Sharing, Game Center, Maps, Messages, Notes, Notification Center, Photo Booth, Power Saver, Reminders, Twitter, iCloud
Video Output
Graphics Processor Intel Iris Pro Graphics 6200
Graphics Processor Series Intel Iris Pro Graphics
Service & Support
Type 1 year warranty
Service & Support Details
Type limited warranty, technical support
Service Included phone consulting
Full Contract Period 1 year, 90 days

Where To Buy

Where To Buy

Apple iMac with 4K Retina display (21.5-inch, 2015)

Part Number: MK452LL/A