How to Speed up your old iMac

I’ve had to deal with this issue many times in my years of working as a professional photographer on various Apple Mac machines. But in the last few years, working on an iMac the methods of speeding things up are fairly limited, but actually very easy to do – and importantly, they are not expensive to do.

Two Main Speed Issues with older iMacs

Memory and Hard Drive speed. Computers need enough memory to not only do a number of tasks in the programs you are running, but also to simply run the Operating System itself. OSX is a very modern operating system, it’s well optimised, but it still needs a certain memory to run it, before you even open up Photoshop or InDesign.

Hard Drives in older machines used to be the old spinning disk variety. Compared to modern SSD drives or even newer NVMe drives, old mechanical drives are painfully slow. Every time you start up your old iMac, if it’s running of an old hard drive, it will take AGES. It should take only seconds with a newer machine or drive.

All wasted time waiting for computers to work is loss of productivity. And anyone that has ever done a time cost analysis will tell you that all of those wasted seconds waiting add up to a lot of wasted money.


All 27″ iMacs are upgradeable, for memory. Doing so is a really, really easy task. And memory is not expensive. The process is as simple as turning off the Mac, popping a push button door on the back, just below the power plug. Then turning a small lever and either removing or adding new memory. I’d recommend nobody with an iMac run it with less than 24Gb memory inside. Preferably 32Gb or more.

The memory is in 4 slots. These are paired slots. 1 & 3 are a pair, and 2 & 4 are the other pair. When adding memory, it’s always done in pairs. Two 8Gb memory sticks (16Gb total) costs around £50-60 at time of writing this (Jan 2022). In an ideal world, you’d have the same size memory in each slot. So all 4 slots would have 8Gb in them for example. However, it will work just fine with a mixed amount. So many original iMacs came with only 8Gb in them, 2 sticks of 4Gb each. Adding 2x 8Gb sticks will bring that up to 24Gb total and the machine will work just fine. It may work faster if you remove the original 4Gb sticks, but the speed saving would have to be balanced with the fact that you might now be using only 16Gb memory. And that could be an issue.

Why not having enough memory is an issue? Well, modern computers are very clever. When they run out of memory, they start using the Hard Drive/SSD as temporary memory. This means that if your machine doesn’t have enough memory, it can use the hard drive. But if your on an old style hard drive (which are pig slow) then you really are running the machine in the worst possible way. It will be dead slow. As memory is so cheap, it’s a no brainer to add more.

How can I tell how much memory I need? Easily. There is a program that comes built into every Mac called Activity Monitor. It’s located in the Utilities folder inside your Applications folder on your Mac. It’s been built into Macs since OSX was created.

Open that program up and you’ll see a screen similar to this screenshot. Click the Memory Tab. This now lists every program running on your Mac, including the system programs running behind the scenes. At the bottom of the page, there is a little box telling you how much memory is in the machine (Physical Memory), then below it is Used Memory. This is how much memory your Mac is currently using. That figure Used Memory should be less than your Physical Memory. If it’s not, then your computer is having to rely on the Hard Drive to give it extra. A really bad way of working.

Memory Usage

External Hard Drives – Boot Drive

It’s not easy to change a hard drive on an iMac. The machines are glued together. It can be done, but personally I wouldn’t bother. The reason being, there are far easier ways to work with a new hard drive. Just use an External Drive to boot from. When I first realised my old iMac was running slow, this was one of the first things I implemented. An external boot drive. If you copy your whole hard drive to a very fast external hard drive, you can then boot from that external drive. This has HUGE benefits to speed.

When people first hear about this method, it can confuse them. I try and think of it this way. The hard drive in your machine, is simply bolted on internally and connected to your motherboard by a cable. An external drive is exactly the same thing, it’s just that you can see the cable. The computer doesn’t actually know where the drive is, physically – and it really doesn’t care.

My current recommendations for an external boot drive would be the Samsung T7 or the Sandisk Extreme Pro (1050Mbs version or 2000Mbs version). Size wise, I’d go for a 1Tb drive. These currently cost around £110 at time of writing (Jan 2022).

Copying your system over to the boot drive is relatively simple to do. You need a program such as Chronosync or Carbon Copy Cloner. Personally I’ve used Chronosync for years and use it for all kinds of other backups. So that would be my choice.

Boot drives need special permissions to run. So you have to ensure the program is set correctly to do the copy. This will take a few hours – possibly even a day or more to do, depending on how much stuff you have on your iMac’s internal drive.

Once done, you can go to System Preferences and choose Start Up Drive. You select the new external drive and restart. The computer now should start from the external drive, not the built in one. How do you know it’s worked? Well, there’s a few ways to check. But one easy way is to go to your user folder. It should have a special icon on it, rather than the standard blank folder icon. The active user folder always has this special icon.

Other benefits? Now that your external drive is the main working drive of your iMac. The internal drive is doing nothing. So you can now use that as a backup drive for your main drive. Chronosync can be set to run once a day, maybe 9pm for example. Then it copies over any new files to the old internal drive. Meaning, that at any point in the future, if your external boot drive dies, you can simply boot from the old slow internal drive. They will always be identical.

Samsung T7 SSD
Samsung T7


Adding more memory and adding an external boot drive are the two biggest factors that will affect the speed of an old iMac. Adding both will cost around £170. I’d consider that money well spent, to keep the Mac going on a bit longer. Of course, buying a new iMac will always be another option, but this is a cheap alternative method to give an old iMac another burst of life.

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