I've got an older iMac running macOs Mojave. It is terribly slow and I am interested to see if we can improve the performance. Can you recommend steps to consider to improve the performance?

The performance issues I see impact the operating system and all applications. It's not specific to a single app.

When viewing the About modal:

  • MacOS Mojave Version 10.14.6 (18G103)
  • iMac 27-inch, Late 2012
  • Processor: 3.2 Ghz Intel Core i5
  • Memory: 8 GB 1600 MHz DDR3
  • Graphics: NVIDIA GeForce GTX 675MX 1GB

Looking at the System Report, I see:

  • Status on Memory Slots is OK. Has 2 4GB 1600 DDR3 cards.
  • Hard Drive: I have about 500GB of available storage on 1TB hard drive

Other than these basic stats, I'm not sure what would be relevant to help diagnose the performance issues on this machine. What information could I provide to help determine the issue? Thank you.

  • 2
    Hi Gregg - many people are going to suggest Memory and drive upgrades. Do you have a good backup and can try to erase the OS and run a benchmark on a clean system? Sometimes you just have brought more work to the same CPU and there is nothing that changed. It’s as fast as running the old easier work, but doing more. Other times, your OS just has a lot of stuff - any chance you haven’t exhausted OS and know how much CPU/RAM is actually needed when you experience bad performance? If you’re network bound, I’d hate for you to upgrade components - same with software bound performance.
    – bmike
    Apr 26, 2020 at 16:15
  • Thanks for the feedback bmike. I will look into this as well.
    – Gregg
    Apr 27, 2020 at 10:58

3 Answers 3


The only two things you can realistically do are change the HD to an SSD & upgrade the RAM.

Some iMacs have GPUs that can be upgraded [slightly] but that's not really going to gain you much.

A 1TB SSD can be bought these days for the price your 1TB HD would have cost back then, approx $£€ 100.
According to Everymac that model can take 32GB RAM. I'd recommend at least 16GB these days.

The SSD alone will put some spring back in its step. The RAM will let it breathe a bit better.

  • How would you be sure it’s not just lots of software slowdowns? I’d love to see a CPU trace or measurable benchmark - many times, it’s just needing a good erase - retest on a clean OS with nothing from years back migrated and piled on.
    – bmike
    Apr 26, 2020 at 16:16
  • @bmike - Noted. When I can afford a PCIe SSD in addition to my existing 2.5" sitting on SATA II, I shall actually do this. Until then, I'm gonna have to just guess. I did get a massive speed increase when I first moved the old Mac Pros from HD to SSD, but I do feel the hit these days of perhaps unoptimised performance. I simply have no easy way to do A/B tests.
    – Tetsujin
    Apr 26, 2020 at 16:19
  • 1
    Additionally, my folks have a 'last of the HD' iMacs from a couple of years ago. At little more than defaults [they only power it up once a month, there's nothing on it] it is the slowest machine [in patience/modern expectation terms] I've ever used.
    – Tetsujin
    Apr 26, 2020 at 16:26
  • I agree - if anyone thinks they have modest needs, an SSD is by far the most massive upgrade you can make.
    – bmike
    Apr 26, 2020 at 17:22

There are basically two things you can do:

  • Get more RAM. There are two free slots, so adding 2x4 GB is easy and having 16 GB instead of 8 GB will make a difference
  • Replace the drive with an SSD

I have a late 2012 Mac mini as my main machine, with 16 GB and a Fusion drive. Definitively not the fastest machine but useable, even with big RAW files etc.

  1. Replace the hard drive with an SSD. I recommend an SSD of at least 1 TB again. Not sure about if this is possible with your iMac either but I had my original 1 TB drive left inside my mid-2011 27” iMac. I am now happily using both drives. My iMac boots from the SSD which has the OS and the programs while my pics, videos and music are on the original drive. If keeping the original drive inside the computer is not possible, you can (have it) put it inside a proper enclosure and use it as an external drive.

  2. Have the RAM increased to at least 16 GB and more if you can afford it.

Each of these two alone should make a big difference and together they should make you feel like you got a brand new computer. Plan ahead well about what to do, especially when adding / replacing the hard drive, and, if you are not already doing so, backup with Time Machine before doing or getting done either.

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