Your 27-Inch iMac Is Slowing Down — And Apple Won't Sell You a Replacement. Here's What To Do.

If you’ve got a 27-inch iMac from any time between 2013 and 2019, there’s a good chance you’re reading this because it’s not as quick as it used to be. Maybe Safari takes an age to open. Maybe the spinning rainbow wheel has become a daily companion. Maybe you’ve noticed Chrome warning you that your macOS version is no longer supported.

You’re not alone. I hear this from clients across East Sussex every single week.

And here’s the part that catches most people off guard: Apple no longer makes a 27-inch iMac. They discontinued it in March 2022, and in late 2023, Apple officially confirmed there would be no Apple Silicon replacement. The 24-inch iMac is now the only all-in-one desktop they sell.

So if your big, beautiful 27-inch iMac — screen, computer, and all built into one — is grinding to a halt, what are you actually supposed to do?

The good news is you’ve got more options than you might think. Let me walk you through them.

Why Your 27-Inch iMac Has Slowed Down

Before we talk fixes, it helps to understand what’s going on. Most 27-inch iMacs from this era shipped with a traditional spinning hard drive — or a “Fusion Drive,” which is part hard drive, part flash storage. Here’s the thing most people don’t realise: spinning hard drives have a life expectancy measured in hours of use. If your iMac is from 2015 or 2017, there’s a very good chance you’ve sailed past the manufacturer’s recommended limit. The drive is still spinning, but it’s tired — and it shows.

On top of that, hard drives absolutely hate being full. If yours has crept up to 80% or 90% capacity over the years — and with photos, documents, and macOS updates, that happens faster than you’d think — performance falls off a cliff. A nearly full hard drive is a slow hard drive, no two ways about it.

It’s not that your iMac is broken. The processor is usually still perfectly capable. It’s just waiting around for that worn-out, overstuffed hard drive to catch up.

The other factor is software. Apple stops supporting older Macs with each new macOS release. If your iMac is stuck on an older version of macOS, you’ll start to see browsers like Chrome and Firefox dropping support too, which means security warnings and websites not loading properly.

But First — Back Up with Time Machine

Before you do anything else, this is without doubt the best time to make sure you’re running regular Time Machine backups. No question. If your hard drive is ageing and potentially running beyond its hours, your data is more vulnerable than you might think. An external drive and Time Machine is the simplest insurance policy you can have. If you’re not already doing this, please start today — before you even finish reading this post.

Option 1: An SSD Upgrade — The Single Biggest Speed Improvement

This is the one I recommend most often, and the results genuinely surprise people.

Replacing your old hard drive or Fusion Drive with a solid-state drive (SSD) transforms your iMac. I’m not exaggerating — a 2017 iMac with an SSD will boot in about 15 seconds and feel responsive in a way it hasn’t for years. Apps open instantly. Files save without delay. The spinning wheel all but disappears.

But here’s an important caveat: whether an SSD upgrade makes sense depends on how much RAM your iMac has. If you’re sitting on 8GB of RAM, an SSD alone won’t give you the full benefit — your iMac will still struggle to keep up with modern demands. You can upgrade the RAM (more on that below), but that’s an additional cost to factor in. If your iMac already has 16GB or more, an SSD upgrade is a no-brainer — that’s the sweet spot where the investment really pays off.

The SSD upgrade does involve a labour cost. At my Ringmer workshop, the charge is £150 for labour and data migration, with the SSD itself on top of that. Your data, apps, and settings all come across — you sit down at your iMac afterwards and everything’s where you left it, just dramatically faster.

If you only do one thing from this list, and your RAM is 16GB or above, make it this.

Option 2: A RAM Upgrade

The 27-inch iMac is one of the few Macs where you can easily upgrade the RAM yourself — there’s a little hatch on the back. Many of these iMacs shipped with 8GB, which was enough at the time but struggles now, especially if you keep several apps or browser tabs open.

Bumping up to 16GB or even 32GB gives your iMac more breathing room to juggle everything you throw at it. If you’re considering an SSD upgrade but you’re on 8GB, getting the RAM sorted first — or at the same time — is essential. Combined with an SSD, it’s like having a new machine.

The Sweet Spot: The 2017 27-Inch iMac

If you’re wondering whether your specific iMac is worth upgrading, here’s my honest take after years of doing exactly this work: the 2017 27-inch iMac with an i5 processor and 16GB of RAM (or more) is the model I’d point to every time.

It’s got enough processing power to handle everything most people need — browsing, email, photos, documents, video calls — and with an SSD fitted, it genuinely feels like a modern machine. It’s also new enough to run macOS Ventura natively, and with OCLP (see below), you can push it further to Sonoma or Sequoia.

If that sounds like your iMac, I’d say without hesitation: upgrade it. You’ll get years more life out of it for a fraction of the cost of buying new.

Option 3: Run a Newer macOS with OpenCore Legacy Patcher

If your iMac has been cut off from macOS updates — meaning Apple says it can’t run Sonoma or Sequoia — there’s a free, community-built tool called OpenCore Legacy Patcher (OCLP) that can change that.

OCLP lets you install newer versions of macOS on Macs that Apple has officially dropped. It works by patching the system in memory, meaning it doesn’t permanently alter your Mac’s firmware. It’s well-maintained, open source, and used by thousands of people worldwide.

Why does this matter? Because running a supported version of macOS means your browsers stay up to date, security patches keep coming, and you don’t get locked out of websites or services that require a modern operating system. It’s particularly important for Chrome, which has been aggressively dropping support for older macOS versions.

One important thing to know: once you’re running OCLP, you’ll need some Terminal commands set up to disable automatic major macOS updates. This is crucial. If Apple pushes a major update and your iMac installs it before OCLP has been updated to support it, you can end up in real trouble — potentially unable to boot. I make sure this is locked down properly for every client I set this up for, so there are no nasty surprises.

I’ve done this for a number of clients and it works well. It does require a bit of technical know-how, which is where I come in — I’ll make sure it’s configured properly, updates are controlled, and everything’s working before I hand it back.

A word of caution: OCLP is brilliant, but it’s not officially supported by Apple. That means you won’t get help from Apple if something goes wrong, and the odd feature might not work perfectly. For most people doing everyday tasks — browsing, email, documents, photos — it’s absolutely fine.

Option 4: A Mac Mini with an External Display

If your iMac really has reached the end of its useful life — perhaps it’s a 2013 or 2014 model and even an SSD can’t justify keeping it going — then the Mac Mini is worth a serious look.

The current Mac Mini is small, powerful, and surprisingly affordable. Pair it with a nice 27-inch monitor (there are good options from LG and others for a fraction of the Apple Studio Display price), and you’ve essentially rebuilt what you had — but with a modern Apple Silicon chip that’ll be supported for years to come.

The bonus? Next time you need to upgrade, you just swap the Mac Mini. Your monitor, keyboard, and mouse all stay. It’s actually a smarter setup long-term.

I can help you choose the right configuration and get your data migrated across from your old iMac. Migration to a new Mac is £120 at my workshop, and that includes setting the whole thing up so it feels just like your old iMac did — just faster.

Option 5: The 24-Inch iMac

I won’t pretend the screen size difference isn’t noticeable — it is. Going from 27 inches to 24 inches feels like a step down, and I understand why people are reluctant.

But the 24-inch iMac is a genuinely lovely machine. It’s thin, quiet, the screen quality is excellent, and the M-series chip inside it is significantly faster than any Intel processor that ever went into a 27-inch iMac. If you can live with the slightly smaller display, it’s the simplest upgrade path — a true all-in-one with no cables, no fuss.

It’s also worth popping into an Apple Store or having a look at one in person before you rule it out. Many of my clients who were sceptical about the size ended up perfectly happy once they’d spent a week with it.

As with the Mac Mini, if you’d like me to migrate your data across from your old iMac, that’s £120 at my workshop — everything transferred and set up ready to go.

So What Should You Actually Do?

It depends on your situation, and that’s exactly the kind of conversation I love having with clients. But as a rough guide:

If you’ve got a 2017 iMac (or newer) with 16GB+ RAM: Get an SSD fitted. This is the upgrade I recommend most confidently — it’s affordable, the results are dramatic, and your iMac could easily have another three to four good years in it.

If your iMac has 8GB RAM: You’ll need to factor in a RAM upgrade alongside the SSD to make it worthwhile. It’s still often cheaper than buying new, but it’s worth having a conversation about whether the combined cost makes sense for your situation.

If your iMac is stuck on an old macOS and Chrome is complaining: OCLP combined with an SSD upgrade is a powerful combination. You get speed and a modern, secure operating system.

If your iMac is from 2013–2014 or has other hardware issues: It’s probably time to look at a Mac Mini with a display, or the 24-inch iMac. Either way, I can migrate everything across so you’re up and running quickly.

Whatever you decide: Make sure Time Machine is running. Today. Not tomorrow.

The one thing I’d say to everyone: don’t assume your iMac is done for just because it’s slow. More often than not, it just needs the right upgrade to feel like new again.

Need a Hand?

I’m Neville, and I run Spurdotech from my workshop in Ringmer, serving Mac users across East Sussex and remotely across the UK. If your 27-inch iMac is struggling and you’re not sure what to do next, give me a call on 01273 985310 or drop me a message through the website. I’m always happy to have a chat and help you figure out the best path forward — no pressure, no jargon, just honest advice.