Old iMac running slow? Check the drive before you replace it
9 November 2026 · Mac guides
An older iMac that takes minutes to start up, shows the spinning beach ball every time you open an app and struggles with a few browser tabs is frustrating. The good news is that on many Intel iMacs the main cause is a single part: the hard drive. This guide explains how to check what is slowing yours down, what an upgrade involves, and when it is better to put the money towards a new Mac.
Why older iMacs get so slow
For years, many iMacs were sold with a traditional spinning hard drive, or with a Fusion Drive, which pairs a small amount of flash storage with a hard drive. Modern versions of macOS are designed with solid-state drives in mind. On a spinning drive, everyday tasks that involve reading lots of small files, such as starting up, opening apps, searching and updating, become very slow. A hard drive that is starting to wear out makes this worse.
Other things can play a part too: not enough free space, not enough memory for the way you use it, a large number of apps opening at login, or a drive that is beginning to fail.
Find out which iMac you have
Choose the Apple menu, then About This Mac. Note the screen size and year, for example "iMac (Retina 4K, 21.5-inch, 2017)" or "iMac (27-inch, Late 2013)". Then open System Information (hold the Option key and choose the Apple menu) and look under Storage to see what kind of drive is fitted. If it says Rotational, or the drive is described as a Fusion Drive, the drive is very likely to be your bottleneck.
Safe checks you can do at home
1. Check free space
Open System Settings, then General, then Storage, or the Storage tab in About This Mac on older versions of macOS. If the drive is almost full, macOS has little room to work and everything slows down. As a rule of thumb, try to keep a healthy amount of space free. Moving old photos, videos and downloads to an external drive can make a noticeable difference.
2. Look at Activity Monitor
Open Activity Monitor from Applications, then Utilities. On the Memory tab, the Memory Pressure graph at the bottom shows whether your iMac is running short of memory: green is fine, while yellow or red most of the time means memory is a real limit. On the Disk tab, a drive that is constantly busy while you are doing very little suggests the drive is holding everything up.
3. Trim what starts at login
In System Settings, under General and then Login Items, remove apps you do not need running all the time. On older versions of macOS this is under Users and Groups.
4. Run First Aid
Open Disk Utility and run First Aid on the startup drive. If it reports errors it cannot fix, or your iMac has started to freeze, make clicking noises or show a folder with a question mark at startup, the drive may be failing. In that case, back up straight away and stop using it heavily.
What an SSD upgrade involves
Replacing an iMac's hard drive with a solid-state drive is often the single biggest improvement you can make to an older Intel model. The difference in day-to-day use is usually obvious from the first start-up.
It is not a home job, though. On most iMacs the glass and screen have to be carefully removed to reach the drive, and on later models the screen is held on with adhesive that needs replacing. It is easy to crack the screen or damage its cables if you do not have the right tools. We carry out Mac hard drive and SSD upgrades and can move your files, apps and settings across, so your iMac comes back looking just as you left it, only faster.
Is more memory worth adding?
If Activity Monitor shows memory pressure in the yellow or red, more memory can help as well. 27-inch Intel iMacs have a small memory door at the back, which makes an upgrade straightforward. On many 21.5-inch models the memory is either soldered to the board or sits behind the screen. Our Mac memory upgrade page explains more, and we can tell you exactly what your model takes.
Upgrade or replace?
An upgrade makes most sense if your iMac is otherwise in good condition, the screen is fine, and it still runs a version of macOS that receives security updates. Apple has said that macOS Tahoe is the last version of macOS for Intel Macs, and only some later Intel iMacs can run it, so check how old your model is before you spend money on it.
If your iMac is too old to receive security updates, or it has other faults as well, putting the money towards a newer Mac may be the better choice. We will tell you honestly which way we would go. Our page on Macs that may be too expensive to repair covers this in more detail, and either way we can help you get your files off the old machine.
Keep your files safe first
Before any upgrade, or if you suspect the drive is failing, back up with Time Machine to an external drive. If the iMac will no longer start or the drive is making unusual noises, do not keep trying to restart it: switch it off and ask us about Mac data recovery, which starts with a free assessment.
Get a quote
Call 020 7394 2525, or bring your iMac to 80 Willow Walk, London SE1 5SY. We are open 9am to 6pm, Monday to Saturday, with bike collection in London and courier collection across the UK.