(this isn't difficult, ANYBODY can do it)
- Get a USB3.1 gen2 enclosure. I have one of these:
12 MONTHS FREE REPLACEMENT AND LIFETIME TECHNICAL SUPPORT: If there was any problem with the products from ORICO Direct Store, please contact us, you will get a free-replacement within 12 months.
- Get an nvme blade SSD, like this:
Silicon Power 1TB - NVMe M.2 PCIe Gen3x4 2280 TLC SSD (SP001TBP34A60M28)
Put the blade SSD into the case, slip the cover on (I found you don't even need to use the screw to keep it closed, works fine without it).
Connect it to your iMac.
The iMac has Mojave, is this correct?
Now, you need to do this:
- open disk utility
- go to the view menu and choose "show all devices"
- select the new SSD by clicking ONE TIME on it (on the left)
- next, initialize (erase) it. Use APFS with GUID partition format
- when done, quit disk utility.
- Next, download CarbonCopyCloner from here:
CCC is absolutely FREE to use for 30 days, this costs you nothing
- Open CCC and "accept the defaults"
- Use CCC to "clone" the contents of the internal HDD to the new SSD. It will take some time to copy everything over, be patient.
- When CCC is done, quit it and open the startup disk preference pane (system preferences).
- click the lock and enter your password
- now click on the new SSD to select it as the boot drive
Do you get a good boot from the SSD?
I'll bet things go much faster now!
A USB3.1 gen2 enclosure will give you read speeds around 960MBps and writes in the 850+ range (at least). The drive will "run warm", but it's normal for these.
Make sure you put the "heat transfer pad" into it before you put the cover on.
One other thing:
The connecting cables that come with many USB3.1 gen2 enclosures can be "on the short side".
You might want to get a longer one -- perhaps so you can use velcro to secure the enclosure to the back of the iMac's stand.
BE SURE when ordering a new, longer USBc cable that it's rated for 10gb per second.