iMac upgrade: SSD external via USB 3.0 vs SSD SATA internal

I am thinking about tackling a project where I open up my late 2012 iMac and installing the same SSD drive I have connected via USB 3.0 (which is what my iMac is currently booting to) into the current HD slot.

My question is…by installing the same SSD into my iMac internally, should all work okay? (I am hearing something about issues with TRIM and perhaps miscalculating heat.) Second question is…will it perform any better?

The reason I ask is that I notice with my current setup (SDD is external and connected via USB 3.0), my iMac occasionally stalls for a split second or sometimes I get the spinning beach ball for several seconds.

Opening up a late 2012 is not an easy task. So, I don’t want to do this unless I will see significant performance improvements.

Any suggestions before I proceed? Thanks.


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SATA would be a little faster, but may not be enough for you to go to the trouble.

Take a look at this:

I’ve got to ask. Is the external SSD you have physically compatible with your iMac? And, are you comfortable with idea you might have to back out the installation?
Since you seem to be considering this because of some minor delays, have you tried doing a clean install of the operating system? I find doing this every few months improves the way my 2011 MacBook Air runs. I’m always impressed how easily I can transfer apps to the clean install simply by copying the backup in the Applications folder. Much easier than Windows.

How can I tell if the external SSD is compatible with my iMac? I thought they were all compatible? For the record, I have a late 2012 iMac and am using this SSD: SanDisk SSD PLUS 1TB Internal SSD - SATA III 6 Gb/s, 2.5"/7mm, Up to 535 MB/s - SDSSDA-1T00-G26.

I actually did a clean install earlier this week. It was working fine at first but now the spinning beach ball is back every so often.

Seeing as I have only removed the HDD from an iMac, definitely not going to profess any expertise. I would highly recommend you visit, and view the correct video for your model iMac. Compare size, shape and connector of HDD they remove with your drive.
Also, note that OWC offers SSD kits including temperature sensor. If you are concerned about temperature problems after installing your drive, that might be a consideration.
I replaced the 256gb SSD in my MBA with a 1tb SSD from OWC. Very happy with it one year on. I can now have both High Sierra and Catalina available without an external drive, and plan on trying to add Win10 soon.
I do note that OWC offers 3 year warranty on their drives.

Oh yeah, spinning beach balls. Running newer MacOS versions on 7 year old hardware has some limitations you have to expect and either put up with, or start saving for new hw.

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Thanks. I have decided not to do the “surgery”. A bit too risky for the small boost in speed. Would be a nice project but I rely on my iMac for work and funds are a bit limited at the moment for a new (or even refurbished) computer.

I’ll just have to put up with the spinning beach ball for a while.


I think that is the right choice for a machine that does not have NVME SSD - USB 3.0 is fast enough in most situations. Still many times faster than a spinning hard drive.