2017 27" iMac: More memory vs. external boot SSD?

I have a 2017 27" Retina 5K iMac with a 4.2 GHz i7 processor, 16GB of memory, and a 2T fusion disk, currently running Catalina. I would like to make things “snappier”, especially when opening applications. I’m not that much worried about boot speed, as I reboot at most once a week or less. Would it be more bang for the buck to double the memory to 32GB (approx. cost $95) or use an external Thunderbolt 3 2T SSD as the boot drive (approx. cost $500), assuming that one had to choose rather than do both? Thanks for any recommendations.

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Absolutely the SSD. It’ll be like a new computer. 32GB RAM will only make it a few % faster outside of enormous tasks.


It depends, I think.
I think the 2TB Fusion drive comes with a128GB SSD, so I don’t know how much improvement you’ll actually see after the honeymoon period.
Smaller Fusion drives had 32GB SSDs and are, well, not good in today’s world.

But, if you want a snappy response when you open apps whilst also running lots of other apps, the RAM could help there.

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Tidbits had an article about one of them adding and external SSD as their boot drive last month. Talked about how it gave their 2017 iMac new life.

I’m on Team External Drive.
A fusion drive gave my 2008 MBP new life, but an SSD was a whole other level of better. Much more so than the ram upgrade I did prior to the drive upgrade.
Not an Apples to Apples comparison (:wink:), but I think you’ll be pleased.

Definitely an external drive - going from 8GB to 24GB in my iMac brought an improvement but nothing compared to the SSD, really did make it feel like a whole new computer.

Note that the Tidbits article was for a 1 TB Fusion Drive, which has the teeny-weeny SSD component.

Just to be clear, I’m not trying to state that changing from Fusion Drive to external SSD will not show a big difference, I’m just suggesting caution considering the OP is going from a top-of-the-line Fusion to an expensive external.

It’s a good point that the benefit of an SSD will depend on how many significant files don’t fit in the SSD portion of the Fusion. My initial post was a bit unqualified. I also see that they’re interested in snappiness-for-the-buck which could mean that the RAM is still the better purchase if it’s only a third as much an improvement as the $500 SSD. So it really comes down to how much of that drive is full (I’m guessing much of it if they want a 2TB SSD) and how often they load something very large into RAM or how often they have enough apps and documents going that frequently accessed swap is an issue.

Team external SSD here…

My first answer was both but the external SSD really is best bang for the buck. If you plan to hold on to this iMac for more than 2 years, I would suggest you add RAM sometime next year and consider replacing the internal spinning HD with an SSD now.

Thanks for your comments, I’ve got my external SSD on order! I’m currently running Catalina; rather than do a clone then upgrade to Big Sur, I think I’m going to do a clean Big Sur installation followed by Migration Assistant from the internal drive. It’s been since 2017 (when I got the iMac) when I last started from a clean install and migration.

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Please let the group know how you got on. I am in the same situation.


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Will do! It’s currently on backorder (I went high end - OWC Envoy Pro FX 2T). I figure you only live once …

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Just a followup. I did a clean install of Big Sur onto the SSD, and when it rebooted after installation, I ran Migration Assistant to bring everything over from the internal Fusion drive. This was by far the longest part of the job. Now I’m up with Big Sur running on the SSD and everything is indeed much faster, in some cases it seems faster than my 2020 MacBook Pro. And I haven’t run into any real issues with moving from Catalina to Big Sur, although it’ll take some getting used to visually.