Which iMac should you buy

Should you go with 21.5- or 27-inch? Should you get 4K or 5K? If you're still deciding on which iMac to buy, we have some advice.

So you've decided to buy an iMac. That's great, but that is only the first decision of many. You'll also need to decide what size display you want, which processor to get, whether you want to upgrade your memory after purchase or just stock your iMac with max memory right from the start, and a whole lot more. We've got a run down of everything you can get with the iMac to help you decide which one is right for you.

Read Rene Ritchie's review of the 2017 iMac

The iMac lineup

Apple's iMac lineup, not including the iMac Pro, comes in three different models. You can get the 21.5-inch iMac with 1080p resolution, the 21.5-inch iMac with 4K Retina display, or the 27-inch iMac with 5K Retina display. On top of that, you can configure your iMac with different processor speeds, graphics cards, storage options, and memory size. The key is deciding which iMac is right for you based on your needs. You don't want to end up spending too much money on an iMac outfitted with specs you'll never even use.

While each model is different, there are a few things that all iMac models have in common. They all have a 3.5mm headphone jack, an SDXC card slot, four USB 3.0 ports, two Thunderbolt 3 (USB-C) ports, and a Gigabit Ethernet connector.

The display size

Size matters, and when it comes to the iMac, it matters for more than just, well ... size. The 21.5-inch iMac supports 1080p at its lowest price model. For $200 more, you can invest in the 4K Retina display model at 21.5 inches in size. The 27-inch iMac is only available with a 5K Retina display, so you don't get the option of choosing something less expensive. It's all-in with the 27-inch model.

You'll get more screen real estate with the 27-inch iMac, but it does come at a price, though the 4K and 5K models both sport the DCI-P3 wide color gamut, so you're getting a lot for your money with the 4K model

If you're planning on using an external monitor alongside your iMac, all three models provide the same resolution support of one 5K external display, two 4K UHD external displays, or two 4K standard HD external displays.

• If you're going to be using one or more external monitors, you might as well get the 1080p 21-inch iMac to save on cost.
• If you want a really fantastic display but don't need a huge display screen, get the 21.5-inch 4K Retina display iMac.
• If you want all the colors and the largest possible display, you want the 27-inch iMac

Note: the 21.5-inch iMac does not have upgradable RAM. Read the upgradable vs. non-upgradable RAM section before making your final decision.

i5 vs i7 processor

Both the 21.5-inch and 27-inch iMacs come standard with an Intel Core i5 processor. The 1080p model features a dual-core processor, while the 4K and 5K iMacs come with a quad-core processor.

What's the difference between two and four cores? Mostly speed — speed at running applications with parallel processing. Apps that use a lot of computation, like 3D model rendering, data transformation, video and audio editing, and even burning DVDs or CDs, will run faster and smoother with four cores over two.

The 4K and 5K iMacs can both be upgraded with the faster i7 processor, which provides an additional speed boost.

The 21.5-inch 4K Retina display iMac can be upgraded to 3.6GHz with a Turbo boost up to 4.2GHz. The 27-inch 5K Retina display iMac can be upgraded to 4.2GHz with a Turbo Boost up to 4.5GHz.

All of the base processor speeds cost $200 more, incrementally, with the exception of the 3.8GHz processor for the 27-inch iMac, which costs $300 more than the next lowest processor tier.

The processor upgrades all cost $200 extra, with the exception of the upgrade from the 3.0GHz i5 processor to the 3.6GHz i7 processor, which costs $300 extra.

• If you only plan on using your iMac for basic stuff, like surfing the web, checking your email, and maybe running some standard productivity apps, you'll be fine with just the dual-core processor of the 21.5-inch 1080p iMac.

• If you will be using some heavy computing programs, like photo or video editing, or burning CDs and DVDs, but don't need an iMac for fully developing programs or rendering 3D games, the standard i5 processor on the 21.5 or 27-inch iMac will do just fine.

• If you need all the speed you can get without switching to the iMac Pro, the 21-inch iMac with the upgraded i7 Intel Core processor is the one for you.

Upgradable RAM vs. non-upgradable RAM

I mentioned above that the 21.5-inch iMac does not have upgradable RAM. When I first decided to buy my iMac, that was my deciding factor in choosing the 27-inch model. I didn't need the extra RAM at first but knew I'd eventually want to upgrade. With the 21.5-inch iMac, you have to decide before you buy whether you want to upgrade your RAM or not.

The 21.5-inch iMacs start off with 8GB of memory, which can be upgraded to 16GB for the 1080p model or up to 32GB for the 4K model. You have to make that decision before you purchase the 21.5-inch iMac.

The 27-inch iMac starts off with 8GB of RAM and can be upgraded to 16, 32, or 64GB before you buy or you can start off small and upgrade at a later date, since the memory card slots are user-accessible.

• If you know now that you'll never need more RAM than what you get when you buy your iMac, you can choose the 21.5-inch model with confidence.

• If you think there may come a time in the future that you might want more RAM or if you just can't afford the upgrade right now, you should get the 27-inch iMac. It's the only one with a user accessible memory slot.

Hard drive vs. Fusion Drive vs. SSD

All models of iMac come with 1TB of internal storage except the highest priced 27-inch iMac (the one with a base processor speed of 3.8GHz), which starts with 2TB of storage.

The difference comes with whether you want a hard drive, a Fusion Drive, or a solid state drive (SSD). So, what's the difference?

A hard drive is a standard mechanical data storage drive. It spins on a central spindle inside the Mac. It's reading and writing speed is determined by its rpm, which is 5400 on the 21.5-inch iMac.

A Fusion Drive is a hybrid of a hard drive and an SSD, or "flash drive" as it is sometimes called. The Fusion drive combines 128GB of flash storage with a 5400rpm mechanical hard drive, which allows for faster reading and writing speeds and also serves as a quick-access storage space for files that are used a lot. Lesser-used files get delegated to the hard drive.

An SSD or flash drive is pure flash and much faster than both a hard drive and a Fusion Drive. It is capable of storing and quickly accessing large files, so you're not waiting for even the oldest of files to load.

Because the iMac comes with two Thunderbolt 3 ports, which are super fast, you can also connect an external drive at a later time if you don't want to invest in one of the more expensive internal storage drives right away.

The 21.5-inch iMac comes standard with a 1TB Serial ATA hard drive and can be upgraded with up to a 1TB SSD for as much as $700 more.

The 27-inch iMac comes standard with a 1TB Fusion Drive and can be upgraded with up to a 2TB SSD for as much as $1,400 more.

• If you think your computing activities are about average, you can get away with the 1080p iMac with the Serial ATA hard drive, but you'll probably want to upgrade with an external hard drive at some point in the future.

• If you don't feel comfortable dealing with an external hard drive for storing most of your files or if you feel comfortable with spending just a little bit more for a much faster hard drive, the 1TB Fusion Drive will go far for you. I never experience slowdown with my Fusion Drive.

• If you're going to be reading and writing all the files all the time, and money is like leaves on a tree to you, go for the biggest and baddest SSD. I mean, why not?

Radeon vs Iris

You may think that a graphics card is only for gamers, but the graphics processing unit (GPU) is the driving force behind rendering everything on your iMac, from the basics of your operating system to photo and video editors to video games.

The lowest end iMac, the 21.5-inch 1080p model, sports the Intel Iris Plus Graphics card, which is nothing to sneeze at, but it's definitely a little outdated by this time compared to the Radeon Pro graphics that come standard on all of the other iMac models. The main difference between the two is that the Radeon Pro chip fully supports virtual reality, which Apple is investing in heavily in the future with macOS High Sierra and later.

As for Radeon itself, you can get a variety of different spec upgrades for the GPU. They all support virtual reality, but it all comes down to speed.

• If you don't play a lot of games on your iMac, and you don't think you'll spend a lot of time editing videos or working heavily with digital photography, you can live with the Iris Pro graphics; they're pretty darn good.

• If you want to invest in virtual reality at any time in the future, if you work with video editing programs, or if you play a lot of video games on your iMac, you definitely want a Radeon chip, and the more graphics-heavy work you do on your iMac, the faster GPU you'll need.

Who should buy the 21.5-inch iMac

The 21.5-inch iMac is the most pocketbook-friendly of the three models. It starts at just $1,099 and is a fantastic computer for everyday use. It's the perfect iMac for those on a budget that use a computer for such things as browsing the web, reading emails, working in productivity apps, and other similar activities. It's a powerhouse of a Mac for the price. It is, however, slowly becoming an outdated model. More and more websites are pushing the 4K and even 5K envelope, and Apple has turned its eye toward virtual reality. So consider your future computing needs. If you don't care about virtual reality and 1080p is good enough for your eyes, you'll be happy with the 21.5-inch iMac.

Just remember to buy the amount of RAM you want right away because you won't be able to upgrade at a later time.

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Who should buy the 21.5-inch iMac with Retina 4K display

The 21.5-inch iMac is the "baby bear" of the line. It's practically just right in every way. It's reasonably priced, comes with the best storage drive and GPU for its price, and is future-proof for advancing technology.

The screen size is ideal for smaller spaces, like apartments or somewhat crowded houses. Even though it's slightly smaller than its big brother, the 27-inch iMac, it's still got a whole lot of screen real estate. If you're going to be connecting an external monitor, the sky's the limit with size and resolution, too.

The specs are the most customizable of all three models, as well. Whether you want to have the base memory, processor speed, graphics, or storage, or you want to go all-in on the top of the line with everything, the 21.5-inch iMac with 4K Retina display has a wide variety of options.

The only shortcoming of the 21.5-inch iMac with 4K Retina display is that the RAM is not user-accessible after purchase, so you'll have to decide before you buy whether or not you want to upgrade your RAM to something more than the standard 8GB.

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Who should buy the 27-inch iMac with 5K Retina display

Until the iMac Pro launches, the 27-inch iMac is the top of the lineup in terms of performance, screen resolution, and speed (not counting the Mac Pro). It's got a fast processor, great storage speeds, a top-notch graphics processor, and post-purchase upgradable RAM. Plus, that screen is something to behold when it's sitting on your desk, all 500 nits brightly smiling at you. It is definitely the most beautiful iMac so far.

But it's a lot of computer to deal with. It's like riding a Thoroughbred when you'd be just fine riding a Shetland pony.

If you spend a lot of time on your computer, if you work in digital content, if you edit videos or photographs, or if you play a lot of video games on your computer, the 27-inch iMac is right for you.

Also, if you want to be able to upgrade your RAM after you purchase, get the 27-inch iMac. I chose the 5K iMac for that singular reason and it was well-worth the extra cost for the additional performance and display screen upgrades.

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Still undecided?

If you're still not sure which iMac is right for you, you should head over to our iMac discussion forums. Our readers are full of great advice and love to share their knowledge and experience with others.