Those who wish to keep these perfectly usable machines usable despite Apple's forced obsolescence. Maybe as one learns how to keep these Macs alive, can spread the word in various ways :)
Some iMacs suffers from poor hardware. Some iMacs suffers from unable to run more modern macOS. Some iMacs have both issues.
HDD (Hard Drive Disk) is much slower than SSD (Solid State Drive) Changing from HDD to SSD instantly makes iMac go way faster. <= 2011 iMacs require internal installation while 2012+ iMacs can just run macOS from external SSD using USB3 speed ports which is quite fast. Not worth the risk of installing SSD internally on 2012+ iMacs with the delicate glued on screen. Very easy to damage and many online directions are misleading/incomplete resulting in screen falling off and cracking :(
Some 2012-2020 iMacs have "fusion" drives. This is a small SSD serving as a cache for the bigger HDD. This design wears out the SSD extremely quickly and will eventually cause iMac to be slower and/or unusable. Solution is same as the HDD, replace the fusion drive system with external SSD
Here is how to tell if you have fusion drive
Disk Utility View All Devices ( link )
Fusion Drive in Disk Utility ( link )
Older iMacs ( <= 2011) can only run macOS High Sierra (HS) or even lower El Capitan. Browers for these macOS are all obsolete and don't work with many websites. This renders these Macs largely useless in the internet age.. There are both easy and a more difficult (with less visual anomalies and faster speed) way to get past HS. Both require learning how to install a hacker community project called OCLP. OCLP basically add back the obsoleted macs drivers to the newer macOS (This is quite a trivialized simple summary, lots of works done by the developers)
Easy :Â Use OCLP to get to newer macOS such as Big Sur ( link ) Some people also choose to run linux or Windows (BOOTCAMP) instead of macOS ( link )
Difficult : Change GPU to one that is metal compatible and use OCLP to installer newer macOS ( link )
Of course 09-11 iMacs internally HDD need to be changed to SSD to gain a real performance benefit. Note these iMacs have different HDD thermal sensor solutions depending on the year and require different workarounds ( link )
Following are minimum effort to make these useful. Hardware upgrades will cost ~$40.
Need to get to 8GB RAM and SSD. Probably $50 total
SSD Purchase ( link )
RAM : 09-11 iMacs have 4 externally accessible RAM slots on the bottom. 12-20 are all >= 8GB. <= mid 2013 Macbooks have easily upgradable RAMs.
If Apple doesn't provide > High Sierra macOS updates (09-11 iMacs), need to learn OCLP to upgrade to at least Big Sur for useful browsers ( link ) If really skilled, can do GPU upgrades ( link )
John Travolta was quite the Disco King back then after Vinnie Barbarino. Maybe a good tune while waiting for the upgrade installation? Maybe installation is even long enough to watch the first 30min of this classic movie haha.
OCLP hackers deserves all the credits. This website is merely a messenger of their hardworks