The 27" has 2 SATA III busses. One takes an m.2 SATA blade and adapter up to 2T; the other takes a SATA SSD up to 4T. Unlike the 2013 and later, there's no speed advantage to installing an m.2 blade in these unless you really want 6T of storage onboard(!),
The HDD is 6 years old and runs hot! hot! hot!. If not worn out yet, it will soon enough. Easy to remove and replace with an SSD. A 2012 will last longer and be more reliable if you do.
Unlike the 2011 and older, Apple has not announced End of Life on these—they support Mojave/Metal Graphics.
In the short term, you can get an SSD and stick it into a $23 USB 3 dock.
https://www.amazon.com/Cable-Matter...qid=1541015692&sr=1-7&keywords=usb+3+ssd+dock
That will work ok but plan on throwing it inside at some point. Mojave doesn't like to run from an external over USB 3—too slow.
[doublepost=1541017898][/doublepost]Here's what you need to replace that spinner with an SSD (besides the SSD, of course).
Tools, tape and a thermal sensor.
https://www.amazon.com/OWC-Digital-...l+sensor+hdd+upgrade+cable+for+imac+2012&th=1
The bracket is recommended but you can get by with double-stick foam tape to the foil lining the back of the housing—I use this bracket:
https://www.amazon.com/Sabrent-Desk...+3.5+adapter#HLCXComparisonWidget_feature_div
The Samsung 860 EVO is very good and comes with a 5 year warranty. $87–$798 depending on size.
https://www.amazon.com/Samsung-500G...f_rd_t=40701&refRID=WZF4W4JT0GX3GK6S9CE3&th=1
You have many choices, some for le$$ unless you want 4T. The 2T WD Blue & SanDisk Ultra (same Toshiba drive) and Crucial MX500 are all quite good and can be had for a little less. Max capacity 2T. Yes the Samsung tests a little better but I bet no one notices any real world difference.
https://www.amazon.com/s/ref=nb_sb_...&sprefix=2T,electronics,202&crid=3PA2L1FSS9ND
I cannot recommend the Micron 1100. It is an OEM (the commercial version is the Crucial MX300). These do not have any warranty if branded Micron as is stated clearly on the Micron web site. The VARs who integrate them into their PCs are expected to handle customer service issues and their costs reflect this. At $288 for 2T, I would avoid since you can get any of the above with a 5 year warranty for very little more.
As long as you're inside, go ahead and replace the NV RAM battery. With the spinner and its heat gone, you can use a common CR2032 medical battery. The high-heat version is the BR2032 and is what Apple installed. $7.98 for one or $8.01 for three:
https://www.amazon.com/Panasonic-Ba...ie=UTF8&qid=1541016659&sr=1-4&keywords=BR2032
Once you install inside the iMac, enable T.R.I.M with the following Terminal command:
sudo trimforce enable Enter your Admin password when prompted and yes to all of Apple's CYA warnings. Yes, you really want to do this.
Although you can run this while booted externally, TRIM does not work over USB of any flavor.
[doublepost=1541018039][/doublepost]
Thanks - how much memory did you upgrade? I was thinking of another 8.
Did upgrading the SSD and memory make a noticable difference?
Memory? If you didn't have enough, yes; otherwise, no.
SSD? Yes if external. Yes! Yes! Yes! if internal.
