21.5in vs 27in iMac

Following Apple (finally) updating the 21.5-inch iMac towards the end of 2015 you may be considering buying one, but is it really a good idea to purchase a 21.5-inch iMac - especially the 4K version, or would you get more for your money if you bought a 27-inch iMac?

Here we will help you choose between the smaller, cheaper iMac and it’s bigger sibling. We will help you decide which iMac to buy, and let you know which iMac is best for your needs.

[Read: 21in 4K Retina iMac (2015) review, plus:  27-inch iMac with Retina 5K display (2015) review]

What is the iMac?

If you don’t already know, the iMac is an all-in-one computer from Apple. It’s been around since 1998 and has had various different designs, but the one thing each design has had in common (apart from being pretty stylish for its time thanks to Apple’s design guru Jony Ive) is the fact that the whole computer is hidden behind the screen.

Many years ago we found a friend scrabbling under a desk wondering where the tower part of the iMac was so they could turn it on, we shouldn’t laugh but this misunderstanding is probably more common than you think, especially now that the Mac’s screen is so slim - people will be wondering just how Apple can fit such a powerful Mac inside that display. And it is a very powerful Mac - although not all iMacs are created equally. Read on to find out the difference.

How much does an iMac cost?

The most obvious difference between the 21.5-inch iMac and 27-inch iMac is the price. And it can be a pretty big difference.

  • The cheapest iMac costs £899
  • For £150 more, we have the mid-range 21.5-inch model for £1,049
  • And for another £150, we have the top of the range 21.5-inch iMac with its 4K Retina display for £1,199
  • Then there’s a bit of a jump up to the 27-inch range of iMacs.
  • The entry-level 27-inch model costs £1,449, £250 more than the top of the range 21.5in
  • Then there is the mid-range 27-inch iMac which costs another £150, at £1,599
  • And right at the top of the range, there’s an iMac that costs an astronomical £1,849 - that’s a whole grand more than the entry level 21.5-inch iMac!

You’ll probably have figured out, having seen these numbers, that there is a big increase in price between the 21.5-inch and 27-inch iMacs. This isn’t just due to the bigger displays, although that is a part of it. There are massive differences in specs between the different models and we’ll go on to explain what those are below.

Where to buy an iMac

You can buy an iMac from the following places, including Apple's High Street stores.

Apple Online

Currys

John Lewis

And various Apple Resellers including KRCS, Stormfront, Solutions Inc, Western Computer and more.

Read: Complete guide to shopping with Apple

21.5-inch versus 27-inch iMac: iMac sizes and screen quality

The most obvious difference between both types of Mac is pretty clear if you are looking at them both together. One has a much larger screen.

The 27-inch iMac has a screen that measures 27 inches from one corner to the opposite corner, while the 21.5-inch iMac screen measures, yes, you’ve guessed it, 21.5 inches.

But there is a lot more than size going on with these screens.

There are two types of screen on the 21.5-inch iMac, the entry-level and the mid-range iMac both have a LED-backlit display offering 1920?by?1080 resolution (that’s a total of 2,073,600 pixels). The screen itself looks stunning, and more importantly makes your photos and videos look stunning. However, Apple goes one better with the top of the range 21.5-inch iMac, it has a Retina 4K display that offers 4096-by-2304 resolution which is an impressive 9,437,184 pixels in total. That’s so many pixels that you’d have to have bionic eyes to see one, and if you have a really high res image and you zoom in on it you will see all the detail, where if you zoomed in using one of the other iMacs that detail would become blurry. For this reason we’d suggest that if your budget doesn’t run to the most expensive 21.5-inch iMac you don’t even look at the screen, because it will spoil you for life!

Of course the screens on the 27-inch iMac go one better with 5120?by?2880 resolution or 14,745,600 pixels. However, it has to be said that Apple has really gone all out on the 21.5in 4K Retina display adding more pixels than anyone really expected and matching the pixels per inch of the 27in Retina iMacs - this means both Macs share the same 217 PPI pixel density.

But all in all you can expect the 5K displays to be superior, the colour accuracy is better on the 27in model and it has an even wider colour gamut than the previous generation of 5K iMac - which means it will deliver 25 percent more colours than the previous one, according to Apple. The 21.5in matches this.

Both the 21.5in and 27in Retina models are 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 can display even more shades of red and green (which means 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.

One long standing criticism is that there’s no height adjustability on the iMac monitors – you can only tilt the iMac back and forth, the only way to raise the monitor if you need to for ergonomics, is to sit it on one of those hard back books you have lying around.

Another criticism is that you can’t just plug the 5K or 4K display of the iMac into another Mac. Not even a Mac Pro. Given that these are essentially the cheapest 4K and 5K displays you can get you can understand why people want to do this! Thunderbolt 3 could allow this so we hope it makes it into the next generation.

21.5-inch versus 27-inch iMac: capacity and storage  

One of the biggest frustrations about the iMac is that with the exception of the two most expensive models, Apple still ships them with a hard drive inside. While some people want lots of storage space and a 1TB hard drive as standard appeals, there is a build to order option (which appears as standard in the mid- and top-of-the range 27in models) that combines a flash (or SSD) drive with a hard drive, so you get the best of both worlds: a big hard drive and a fast flash drive which means your Mac and your frequently used applications can start up really quickly. Essentially with a Fusion Drive your Mac will run faster. The Fusion Drive update is only £80 extra when you purchase an iMac so we strongly advise that you buy it! Our one complaint is that while Apple has bought the price of the Fusion Drive down it’s changed the default size of the SSD that comes with it to a measly 24GB where it used to be 128GB. Having reduced the price so much we really cant understand why Apple hasn't just thrown it in as standard.

Another thing you need to know is that the storage in the 21.5in iMac is really really poor in comparison to the storage in the 27in version. Apple is using what is essentially a laptop hard drive in those 21.5 models, and that means it runs at 5400-rpm, while the hard drive in the 27in iMac runs at 7200-rpm.

A much better idea is to get a SSD drive at the point of purchase. When you buy a Mac from Apple you can specify various updates, and we recommend you pick an SSD drive or a Fusion Drive, but please don’t go for the Hard Drive unless you really really really need 1TB of space. You might think you need a load of space but you can probably store things like your music and photo library on an external hard drive and enjoy the massive speed improvement when you use your Mac. We’ll say no more on the matter.

21.5-inch versus 27-inch iMac: Graphics

One of the key differences between the 21.5in and the 27in iMac is that the bigger model offers a dedicated GPU (graphics processing unit) 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.

In the 21.5in iMacs you’ll find Intel's own GPUs integrated on the processor itself. Because there’s not a dedicated GPU on the 21.5in iMac you can’t expect the graphic performance to be as good as that which you would get from a AMD (or Nvidia) graphic chip. So if you are looking for a Mac to play games on then the 21.5in models are definitely not for you.

Unfortunately the AMD chips, while a lot better than the integrates chips are themselves not really up to the standards of  dedicated gaming PC, although it will be able to handle some mainstream games at a lower resolution setting. If you try and play games at the full 14 million pixels expect there to be a lot of stuttering.

21.5-inch versus 27-inch iMac: processor

Speaking of the integrated graphics in the 21.5in model, they are responsible for another thing that lets down that iMac. The processor Apple is using is a generation older than the processor in the 27in iMac. Where the new 27in iMac uses Intel’s new Skylake processors, running at 3.2GHz and 3.3GHz, depending on which model you choose, the 21.5in model uses an older Broadwell processor with the entry-level model running at a mere 1.6GHz - don’t buy this model, the next one up has a 2.8GHz processor and only costs £150 more, you’d be crazy to opt for 1.6GHz (that processor would normally be found in a laptop - so why not just buy a MacBook Air!)

The 4K iMac has a 3.1GHz processor, but like it’s smaller siblings it’s a Broadwell not a Skylake.

Now you know this you probably can see why the extra expense of the 27in iMacs is justified. However, we expect that there will be new 21.5in models coming this summer which will have Skylake processors, so it will be interesting to see what happens there.

Read: How to choose the best processor for your Mac

Who is each iMac designed for?

Just because the 27in iMac is better than the 21in iMac doesn’t mean that it will be the best Mac for you. That all depends on your needs. If you are just sending emails and surfing the web and Facebook then you really don’t need a 27in iMac.

If you are a designer or a photographer, or someone who needs more power, then the 27in iMac is a good choice. Just don’t lumber yourself with a hard disk, trust us!

Read:

Buying advice: Best Mac for graphic design

Best Mac for Students

Which iMac should I buy?

If we were to choose an iMac we’d probably consider the £1,199 with the 4K display, but we’d up the RAM to 16GB (another £160) and either get that Fusion Drive (£80) or, more likely, get 256GB Flash Storage for £160. That would bring the total price to £1,359.

Of course at that point you need to stop and think about whether the entry level 27in iMac which costs another £90 would be a better choice - but then you’re still want that extra RAM and the Fusion or Flash drive…

If you need a cheap Mac, we recommend the Mac mini (although we are hoping it will get an update from Apple soon so we’d hold off for now) or the MacBook Air, both of which are cheaper than the iMac with equivalent specs. Another good option would be the entry-level 13in MacBook Pro which also has a high-res Retina display.

Wondering which Mac to buy? Read our full guide: Best Mac to Buy

Want to know how to set up your new Mac? Read: Mac tips and tutorials: everything you need to know to set up your new Mac

Also: Buying advice: MacBook laptop versus Mac desktop

OUR VERDICT

With the exception of the best two 27in iMacs Apple continues to lumber it's Macs with hard drives, we really wish it would make the Fusion Drive standard across the whole range. While we love the new 4K screen on the 21.5in iMac, once you have upgraded it with the necessary Fusion Drive (or flash drive) and some extra RAM it costs almost as much as the entry level 5K iMac. The 27in iMac is a great choice if you are a creative looking for a fantastically speced Mac, but if you are looking for a cheap Mac there are better options than the entry-level 21in model.

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