* The Late-2011 iMac is the last one with an optical-drive.
* The Mid-'11 i7 is the most reliable FAST machine that's east to take apart.
* The early-2009 blackback iMac 24" C2D is the oldest machine that ran run a dosdude-patched Mojave with both hardware-acceleration and wifi enabled.
* The 2012 to 2020 27" machines have the same chassis, but vary widely in internal components. Retina displays were an expensive upgrade option; base models had standard 2k displays. Some screens also had an anti-glare coating that was easy to scuff (and was a pain to remove once scuffed).
* 2012 iMacs are the first with USB3.
* 2012 to 2014 models with 121gbSSD/1TBor3TB 7200rpm Fusion drives were the top models. My favorite machine of this era is a Late-2013 27" 3.5ghz i7 with 500gb SSD and a bright 2k screen perfect for watching 1080p movie rips. With Mojave running in an HFS+ partition, you'll be very happy. The processor and video-card easily handle "shrinking" 4k blue-ray content in VLC Media Player.
* Retina displays debuted in, IIRC, 2014.
* "Cripple-chips" hit the market in 2014; these contained 'failed' processor chips with one defective bank of the silicon wafer blocked off during manufacture. These had a rated speed of half that of a "good" chip, i.e., 1.8ghz was half of a 3.6ghz, but performance was even worse than half due to lack of multi-threading. One of the slowest computers that Apple ever made was 21.5" iMac with a 1.4ghz i5 cripple-chip and a 5400rpm rotational drive; these turkeys were dumped on schools and libraries where they just had to sit turned on 24/7 running book check-out software and web-browsers. These glacially slow lemons were rated kosher for MacOS Monterey, while screamer i7 2012s and 13s were denied it.
* As far as I know, the cripple-chips were only put in 21.5" iMacs, MacMinis, and Macbook Airs (where their presence was more tolerable in conjunction with an SSD).
* 2015 saw a top-model performance gain with top i7 processor going to 4ghz but also a noticeable performance hit with Fusion drives throttled to 24gbSSD/5400rpm. (Base models lacked SSDs regardless.) The 2015s are the last year in which a 27" LED Cinema Display or Thunderbolt Display can be plugged straight in without any problems.
* 2017 saw a top-model performance gain with 4.2ghz i7s and DDR4 ram. 2017 was the first year with USB-C, but also retained the older style USB ports as well. On a sad-note, 2017s no longer play the Macintosh startup chime.
* 2019 saw the fastest top-model of the entire series: an i9 beast with a 1TB SSD. In appearance it was identical to the base model lemon 3ghz i5 with 5400rpm rotational-drive. 2019s were USB-C only.
= = = =
Guide to Getting Your Money's Worth
1. You will run MacOS Mojave in an HFS+ partition on any 2012+ 27", or High Sierra on the older DVD-slot models.
This set-up runs considerably faster than Catalina/laterOS running in APFS, no matter what type of drive you have. You will patch the OS to turn off notifications, disable MRT, disable Spotlight indexing, and disable iWidget syncing, enable apps from anywhere, and in general make your life much more pleasant. Remove Adobe and Microsoft gunk from the library/daemon folders. Take Safari, Mail, and News off the dock; replace them with Vivaldi, Opera, or some other browser still taking updates in 2023. Get the Adblocker Ultimate and ublock-origin browser extentions. Wean yourself off Apple's built-in planned-obsolescence app rubberwalled-isolation-room ecosystem, and never see an ad on Youtube ever again. Install VLC Media Player and make it default for all picture, audio, and movie formats. Get an external drive, create HFS+ partitions on it, and set Carbon Copy Cloner 4 or 5 to clone the OS daily (verify that it boots). Other old abandonware utilities to acquire: DriveDx and DiskWarrior.
2. Used price differences between i7s and i5s, and various drive types, aren't much for 10yo computers (because their second-hand sellers usually don't know the difference), but the performance differences are huge. A 2012 3.4ghz i7 with a Fusion drive will smoke a 2019 base model rated kosher for Ventura (which would strangle the thing).
3. For a general puttering around desk machine that won't be turned off iften, anything will do, even the slowest i5 w/rotational-drive. Your computer is a sports-car idling at a stop-light waiting for the tortoise-human to infrequently tell it to go fast, so it doesn't matter if you have a Ferrari or a Civic. All that matters is that the screen is bright, and there's enough memory to run the OS reasonably well. (If set up as I describe in #1, 8gb of ram is all you need.)
4. If you have hawk-like vision enough that 4k is important, then any Retina will do. (
But beware eyestrain, as some people seem to experience.)
5. If you cannot survive without 64bit bloatware subscription-model software versions of your favorite application suites, then you'll probably need 16gb or more ram.
7. If you render or "convert" video professionally (and for some reason want to do it in an iMac rather than MacPro tower package), get a 2017+ i7 or an i9 for vastly greater rendering performance, or at least an i7 in general. If you simply stream-copy cut-n-join video, then anything will do.
8. If you frequently turn the machine on and off, and create or copy mass quantities of files, then get a machine with a Fusion drive or full SSD.
Lastly, a word about fragility: Apple knows that you are going to chip or crack the glass on these things, and has made it a *bitch* to deal with, because planned-obsolescence. If you're a klutz, get an "otterbox" for your iMac, or make one yourself.