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Apple iMac with 4K Retina display (21.5-inch, 2015) review: Apple packs more pixels into its smallest iMac

The 21.5-inch Apple iMac all-in-one steps up to a 4K display.

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Dan Ackerman
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Dan Ackerman

Editorial Director / Computers and Gaming

Dan Ackerman leads CNET's coverage of computers and gaming hardware. A New York native and former radio DJ, he's also a semi-regular TV talking head and the author of "The Tetris Effect" (Hachette/PublicAffairs), a non-fiction gaming and business history book that has earned rave reviews from the New York Times, Fortune, LA Review of Books, and many other publications. "Upends the standard Silicon Valley, Steve Jobs/Mark Zuckerberg technology-creation myth... the story shines." -- The New York Times

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Last year's addition to the 21.5-inch Apple iMac line caught our attention by cutting the starting price to $1,099 (£899 or AU$1,349) and positioning itself as essentially a MacBook Air recast as a desktop system; the new version for 2015 aims higher.

apple-imac-with-4k-retina-display-21-5-inch-2015-22.jpg
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Apple iMac with 4K Retina display (21.5-inch, 2015)

The Good

Apple upgrades the 21.5-inch iMac with a stunning 4K-resolution display, along with faster processors and Thunderbolt 2. The redesigned keyboard, mouse and trackpad all have rechargeable batteries and lightning connectors.

The Bad

The new processors are still one generation behind Intel's latest and there are no discrete graphics options. No HDMI input means it can't double as a TV monitor.

The Bottom Line

The smallest Apple iMac trades up to a 4K display, and jumps to newer, but still not the latest, processors. While the design hasn't changed, newly crafted accessories with rechargeable batteries and Lightning connectors add flair and convenience.

The flagship device in Apple's just-updated late-2015 iMac line is the configuration reviewed here, stepping up to a gorgeous 21.5-inch 4K resolution display and starting at $1,499 in the US (£1,199 or AU$2,099). Two other base models, at $1,099 and $1,299, retain their 1,920x1,080 displays.

Sarah Tew/CNET

It's worth noting that this is the more literal implementation of 4K in the new 21.5-inch iMac. The display resolution is 4,096 pixels wide, rather than the more common consumer version (sometimes called ultra-high definition or UHD), which has a just slightly lower resolution and is 3,840 pixels wide. That says to us that this system is targeting professional (and high-end enthusiast) photo and video users, who may shoot at that higher version of 4K resolution.

Your big, fancy 4K television set, and every other 4K computer we've seen to date, all adhere to the more consumer-targeted 3,840x2,160 version of 4K. The 4,096x2,304 on this new iMac screen will play any of your 4K content just fine, although the tiny difference in native resolution can have a small scaling effect, which we really only noticed when viewing 3,840-resolution test patterns.

The big secret about 4K is that a lot of people buy a 4K TV, monitor or computer, without really planning on viewing much 4K content on it. It's just the latest spec upgrade to strive for, and most of your video content, and even video games, aren't going past standard 1,920x1,080 high-definition anytime in the near future.

Sarah Tew/CNET

But higher-res screens such as the 4K display here have other advantages. As we saw with the 5K display on last year's 27-inch iMac , individual pixels are practically invisible to the naked eye. On-screen text looks sharper and clearer than on lower-resolution screens, and Apple's expert scaling always keeps apps, menus and icons at a decent size, while giving you the option to mimic the look and feel of several different scaled resolutions. It's the same system Apple has used in all its Retina display models, going back to the MacBook Pro with Retina display.

But there's more to the new iMac than just a higher resolution. The new Retina display supports the wider P3 color gamut versus the more common sRGB (standard Red/Green/Blue) version. Translated for the rest of us, that means the display can show more of the green and red color spectrum (blue, the third leg of the color triangle, is already fairly maxed out under RGB). Apple says it adds up to 25 percent more available colors to display.

P3 is the standard for digital cinema projection in theaters, and for certain photo professionals and film and video experts, this is potentially a big deal. For photo hobbyists, you're unlikely to be able to appreciate the difference, as very little consumer-grade equipment is going to give you files that can take advantage of the wider P3 color gamut (some dSLR cameras, however, can). However, in side-by-side testing using some sample images, the effect was subtle but impressive, with richer reds and greens, and Apple's photo apps as well as third-party programs such as Photoshop, all support color far beyond standard sRBG.

It's little surprise that the new 21.5-inch Apple iMac looks 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.

But inside the familiar convex chassis of the iMac, there are some important spec changes for 2015. All three 21.5-inch models jump from Intel's fourth-generation Core i-series processors to newer fifth-generation chips. That's important because these iMacs were previously two generations of CPU behind. However, only the 27-inch iMacs, now all featuring the high-res 5K display, move up to the very latest CPUs, from Intel's recent sixth-generation of Core chips, sometimes known by the codename Skylake.

Sarah Tew/CNET

It's a shame the iMacs are still one chip generation behind, especially with nearly every consumer PC hitting stores this holiday season moving to Skylake chips. But, for a desktop system it's less important, as actual performance changes between generations of Intel chips are fairly modest. Most of the advantage comes in battery life, and for an all-in-one desktop, that's not going to be an issue.

Also new in the 21.5-inch iMac are Thunderbolt 2 ports for faster data transfer (if you have any Thunderbolt-equipped accessories) and some new hybrid hard drive options -- Apple calls them Fusion drives -- combining a small amount of solid-state memory for quick access of frequently used data, with a larger standard platter drive.

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 Apple wireless Keyboard, Magic Mouse and Magic Trackpad -- all familiar sights on Apple users' desks around the world -- have gotten their first overhaul in years, and it might be the new feature I'm most excited about.

Say hello to Apple's new Magic Keyboard, Magic Mouse 2 and Magic Trackpad 2 for the Mac (pictures)

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All three lose their reliance on disposable batteries, instead moving to internal rechargeable lithium-ion batteries. That allows the keyboard and trackpad to slim down, removing the bulbus 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 to 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.

CNET/Sarah Tew

Overall, this is an important update to the iMac line, as a better-than-HD display feels like table stakes these days for any premium laptop or desktop computer, and the improved color gamut support in the 4K and 5K displays will help keep the iMac line as a top choice for creative pros.

For everyone else, even if you don't regularly view 4K content, a sharp-looking Retina-level display is one of those things that's nearly impossible to give up once you get used to it, and the new 4K iMac is competitively priced with the handful of 4K-display Windows PCs we've reviewed.

If you have a model from the past few years, this isn't a must-have upgrade, but it may certainly be worth picking up the new keyboard and mouse or trackpad to give your older iMac a facelift.

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

Price as reviewed $1,499
Display size/resolution 21.5-inch 4,096x2,304 display
PC CPU 3.10GHz Intel Core i5-5675R
PC Memory 8GB DDR3 SDRAM 1866MHz
Graphics 1536MB (shared) Intel Iris Pro Graphics 6200
Storage 1TB 5,400rpm HDD
Networking 802.11ac wireless, Bluetooth 4.0
Operating system Apple OS X 10.11 El Capitan

Design and features

You can read any of our iMac reviews over the past three years to get a feel for the long-standing design of this high-end all-in-one. It still manages to look current, although some newer trends seen on the Windows side, from thinner bezels to touch screens, are absent here.

The iMac is dominated by its display, which also houses all the system components. It's still just 5mm thick at the edge, gently bowing out in the back. It looks almost paper-thin when viewed from the correct angle, and still pretty svelte even in full profile, where the rear panel bows out in the center into a gentle bowl shape.

That top section is connected via an adjustable hinge to a curved one-piece stand. If you're not connecting any external USB, Thunderbolt 2, or Mini-DisplayPort devices, and using Wi-Fi instead of a wired Ethernet connection, this is essentially a one-cable setup with a single white power cord in the lower middle of the back panel. As with most Apple computers, this is a sealed system, with no user-accessible components -- unlike the 27-inch iMac, which has an access port for the RAM slots.

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Watch this: Meet Apple's new keyboard, trackpad and mouse
Meet Apple's new keyboard, trackpad and mouse
2:27

Thinner, lighter accessories

The biggest physical change is in the new packed-in accessories, named the Magic Keyboard, Magic Mouse 2 and Magic Trackpad 2. As before, the keyboard and mouse are included by default, but you can choose to swap in the Trackpad instead of the mouse. With these new versions, however, the adding the Trackpad costs extra. All three are also sold separately, at $79 for the Magic Mouse 2, $99 for the Magic Keyboard and $129 for the Magic Trackpad 2 (all prices in US dollars). Previously, all three first-gem accessories were sold by Apple at $69 each.

That's a big jump in price for the trackpad, but it's easily the most impressive of the new accessories. The pad goes from aluminum-colored to off-white, and looks and feels massive. Apple says the surface area is 29 percent larger. Without the the cylindrical battery compartment, the pad has an even more minimalist look, lying flat on the tabletop with a slight wedge shape.

Sarah Tew/CNET

The Magic Trackpad 2 supports Force Touch, the new touchpad mechanic found in the MacBook and MacBook Pro laptops (a variant is also now in the iPhone and Apple Watch). Force Touch uses four corner sensors to replace the hinged "diving board" mechanism found in most touchpads, including Apple's previous ones.

A deeper dive into how Force Touch works and what it can do can be found here. The sensors allow you to click anywhere on the pad's surface with identical results, and the Force Click effect, which combines the sensors with haptic (or taptic) feedback, allow you to have two levels of perceived clicking within an app or task. It can be used to bring up context-sensitive content when you use the firmer, double-level click on files or individual words, from pop-up previews to dictionary definitions to Apple Maps directions.

Sarah Tew/CNET

The Magic Keyboard also loses the cylindrical battery compartment, and now sits flat on your desk as well. The overall footprint is 13 percent smaller according to Apple, the key faces themselves are slightly larger and have a new scissor mechanism under each key. The top row of function keys has graduated to full-size from the half-height keys on the previous Apple keyboard. In hands-on use, typing feels very similar to the older keyboard, and also similar to typing on any Mac keyboard, save for the wide, shallow keys of the 12-inch MacBook.

The Magic Mouse 2 is the least changed of the three accessories. Its body remains the same, but the rubber runners on the bottom panel have been tweaked for smoother gliding over your table or mousepad. The minimalist design has its fans, but it's never been my favorite mouse, and for years I've recommended swapping it out for the trackpad. It's a shame the Magic Trackpad 2 costs more now. I'd still choose it over the mouse, but die-hard mouse fans may disagree -- as they very vocally have when I suggested the mouse era was over or that touchpads were naturally superior, even for desktops.

Sarah Tew/CNET

All three rechargeable accessories connect and charge to one of the iMac's USB ports via a standard Lightning cable, and a full charge should last a month or more, according to Apple. Connecting via Lightning also pairs the accessory with the system, so you don't have to search for it though the Bluetooth menu. These will also pair and work with existing Macs that have Bluetooth 4.0.

4K, with a professional twist

You can easily add the new keyboard, trackpad or mouse to your current iMac. The real selling point here is that this is the first 21.5-inch iMac with a 4K display. At 4,096x2,304 native resolution, it contains 9.4 million pixels, which is more than four times the number of pixels in a standard 1080p HD display (Apple's 27-inch 5K iMac has 14.7 million pixels).

As with all of Apple's Retina-class displays (the name Apple uses for its better-than-HD displays across laptops and desktops), the real difference comes when you use one for a while and then go back to a lower-resolution display. You're suddenly aware of individual pixels, and how on all of Apple's Retina screens they're essentially small enough and numerous enough to be invisible. The same basic point goes for the handful of 4K or nearly 4K laptop screens we've seen on Windows systems, including the upcoming Microsoft Surface Book (which has a 3,000x2,000 resolution).

For working on 4K video, that means you can preview your work full screen at full resolution. For photo editors, it means more pixels on the screen at once, instead of endless zooming and navigating. For casual Web surfers, it means even basic black text on the white background looks crisper and clearer, which may mean less long-term eye strain.

Sarah Tew/CNET

With the help of CNET TV and video expert David Katzmaier, I loaded up a series of 4K videos and test patterns. The 4K videos, mostly scenes of natural landscapes or picturesque architecture, looked great, to no surprise. The IPS (in-plane switching) panel also made sure the images looked crisp and didn't fade when viewed from side angles. Katzmaier's expert eye, however, did note that there was a slight scaling effect going on when viewed inches from the display. And he was right -- nearly all the 4K consumer-level footage you're likely to find is at the more common 3,840x2,160 UHD resolution, and when viewed full screen, some scaling needs to happen. We confirmed this by firing up a 3,840x2,160 test pattern and saw the same scaling we observed in last year's 5K iMac.

But unless you spend a lot of time staring at 4K test patterns, it's a largely academic issue. Nearly all of the content you're likely to view on this system, from games to online video, will be upscaled from 1,920x1,080, and still look fantastic and pixel-free. That's especially important on a display that will likely be only a foot or so from your face, as opposed to a 10-foot 4K TV experience, where the benefits of 4K are more dubious.

Yes, you can still save a few hundred dollars and get the older 1,920x1,080 display, but from our phones to our televisions to our tablets, shoppers are acclimating to higher resolutions, and moving up to this great-looking 4K display provides a certain measure of future-proofing.

Ports and connections

Video mini-DisplayPort/Thunderbolt (x2)
Audio Combo headphone/microphone jack
Data 4 USB 3.0, SD card reader
Networking Ethernet, 802.11ac Wi-Fi, Bluetooth 4.0
Optical drive None

Connections and performance

In a single row on the back of the chassis is a collection of ports and connections, including four USB 3.0 ports, two Thunderbolt/mini-DisplayPort connections, an SD card slot, Ethernet jack and a headphone plug. The only real difference this year is that the Thunderbolt ports have been upgraded from the original Thunderbolt spec to the newer Thunderbolt 2. Missing is USB-C, the small, reversible plug found in the 12-inch MacBook and a handful of Windows PCs. Between this and the new Beats Pill+ speaker, it certainly seems as if Apple is betting big on Lightning as its default connector, rather than USB-C.

Sarah Tew/CNET

With the new 4K iMac, you're stepping up from Intel's fourth-generation Core i5 and Core i7 processors to the fifth generation. In codename terms, that's going from Haswell to Broadwell. But, that's still one step away from the chips just starting to ship in consumer laptops and desktops this fall, the sixth generation of Intel's Core chips (yes they also have a codename, Skylake). Those brand-new 2015 processors are found in the more advanced 27-inch iMac models, but the 21-inch systems are a full generation behind.

That may not do much for your bragging rights to having the most updated computer on the block, but it's also not something that's going to have a huge impact on day to day use for most people. The big secret of the computer biz is that processors from even a few generations ago are perfectly fine for the work most of us put our systems through. There's been a huge shift over the past several years towards cloud-based tools that run in a Web browser, from Web-based email to online productivity suites such as Google Docs and Microsoft's online Office apps. Beyond that, we spend a lot of time on social media and online media streaming, all of which are considered rather lightweight tasks.

The real benefit, year over year, of having the latest Intel processors, is improved power-efficiency and better battery life, which are more important for laptops and hybrids than for desktops.

In our CNET Labs benchmarks, this new 4K iMac with a 3.1GHz Intel Core i5-5675R CPU performed on par with other recent Core i5 systems, showing the minimal performance jump between generations of Intel chips in the everyday tasks we use to test. It was about as fast as last year's big 27-inch 5K iMac, although no doubt the new Skylake-powered 27-inch models would be faster. Bringing up the rear is the latest Apple laptop, the 12-inch MacBook, which runs a rarely used Intel chip called the Core M that has, so far, underwhelmed in the handful of systems we've seen it in.

In hands-on use, the new iMac felt very zippy, even when playing back 4K video files, manipulating large photo files, or jumping between multiple browsers and multimedia apps.

While the 27-inch systems offer discrete R9 graphics from AMD, the 21-inch models now only include Intel's default graphics hardware. Last year's higher-end 21-inch iMacs included Nvidia GeForce 750M graphics, but that was already a well out-of-date graphics chip a year ago (the current equivalent would be the GeForce 950M -- for mainstream gaming we'd suggest at least a 960M GPU).

Sarah Tew/CNET

So while you can play back and even edit 4K video on the new iMac, a gaming machine this is not. In a casual gaming test, we ran Tomb Raider at 1,920x1,080 resolution and medium graphics settings and saw a playable 30.3 frames per second. Just for the sake of curiosity, we ran the same game at the full 4K resolution, and it scored a mere 6.7 frames per second.

Conclusion

The pitch for this revamped Apple iMac is pretty simple: Take last year's high-end base configuration, upgrade it to a 4K display and newer (although not the newest) processors, while keeping the price the same. Adding to the appeal are the newly redesigned included accessories, Thunderbolt 2 and more hybrid hard drive options. The lower-cost base model 21-inch iMacs get most of the same refinements, minus the new display. One letdown is that the very basic Nvidia graphics card from the previous $1,499 configuration has been removed.

If you have a relatively recent iMac, and aren't heavily invested in 4K video editing or super-high-resolution photography, there's not a compelling reason to upgrade. Refreshing your keyboard and mouse or touchpad would be very tempting, but those new accessories are also sold separately. If you're a true power user, you're probably already leaning toward a 27-inch iMac (especially now that the entire line has 5K Retina displays) or even a Mac Pro desktop.

But if you're looking for a mid-range all-in-one with high-end feel, and one of the best-looking displays we've seen, the 4K upgrade is worth a little extra investment, and should age well over the next few years, especially as we move further and further into the 4K era.

Handbrake Multimedia Multitasking test

Apple MacBook Pro (15.6-inch, 2015) 149Apple iMac with 4K Retina display (21.5-inch, 2015) 153Apple iMac with 5K Retina display (27-inch, 2014) 155Toshiba Satellite P50t-BST2N01 181Apple MacBook (12-inch, 2015) 465Apple iMac (21.5-inch, 2014) 466
Note: Shorter bars indicate better performance (in seconds)

Adobe Photoshop CS5 image-processing test

Apple iMac with 4K Retina display (21.5-inch, 2015) 170Apple iMac with 5K Retina display (27-inch, 2014) 177Apple MacBook Pro (15.6-inch, 2015) 190Toshiba Satellite P50t-BST2N01 197Apple iMac (21.5-inch, 2014) 270Apple MacBook (12-inch, 2015) 307
Note: Shorter bars indicate better performance (in seconds)

Apple iTunes encoding test

Apple iMac with 5K Retina display (27-inch, 2014) 52Apple iMac with 4K Retina display (21.5-inch, 2015) 57Apple iMac (21-inch, 2014) 78Toshiba Satellite P50t-BST2N01 90Apple MacBook Pro (15.6-inch, 2015) 97Apple MacBook (12-inch, 2015) 130
Note: Shorter bars indicate better performance (in seconds)

System Configurations

Apple iMac with 4K Retina display (21.5-inch, 2015) Apple OS X 10.11 El Capitan; 3.1GHz Intel Core i5-5675R; 8GB DD3 SDRAM 1866MHz; 1536MB (shared) Intel Iris Pro Graphics 6200; 1TB HDD
Apple iMac (21-inch, 2014) Apple OS X 10.9.3 Mavericks; 1.4GHz Intel Core i54260U; 8GB 1,600MHz DDR3 SDRAM; 1792MB (shared) Intel HD Graphics 5000; 500GB HDD
Apple iMac with 5K Retina display (27-inch, 2014) Apple OS X 10.10 Yosemite; 3.5GHz Intel Core i5-4690; 8GB 1600MHz DDR3 SDRAM; 2GB AMD Radeon R9 M290X; 1TB Fusion HDD
Apple MacBook Pro (15.6-inch, 2015) Apple OS X 10.10.3 Yosemite; 2.5GHz Intel Core i7-4870HQ; 16GB DDR3 SDRAM 1600MHz; 2GB AMD Radeon R9 M370X; 512GB SSD
Apple MacBook (12-inch, 2015) Apple OS X 10.10.2 Yosemite; 1.1GHz Intel Core M-5Y31; 8GB DDR3 SDRAM 1600MHz; 1536MB Intel HD Graphics 5300; 256GB SSD
Toshiba Satellite P50t-BST2N01 Microsoft Windows 8.1 (64-bit); 2.4GHz Intel Core i7-4700HQ; 16GB DDR3 SDRAM 1600MHz; 2048MB (dedicated) AMD R9 M265X; 1TB Hybrid HDD

apple-imac-with-4k-retina-display-21-5-inch-2015-22.jpg
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Apple iMac with 4K Retina display (21.5-inch, 2015)

Score Breakdown

Design 8Features 9Performance 8