There is a size “B” card for the 27” iMacs and a size “A” card for the 21.5” Macs. There are 2 cards that I have found which offer boot screen and Metal support. Unfortunalty with these iMacs, It can be done but requires a more up to date graphics card. Special credits must do to DosDude who created the Mojave and Catalina Patcher tools to allow people to run these operating systems on their older unsupported Macs. Note, As this guide is now over 3 years old, time has marched on and not been kind to our 2009-2011 iMacs, The main issue we are all facing is the lack of Metal support with the AMD cards (If they haven’t failed already) As most of you are probably all aware, there are some great developers on the scene that have devoted a lot of time into keeping our old unsupported Macs on the road. Good luck and save yourselves a few quid.ĮDIT - The M8900 Firepro is the same card so can be flashed with the Apple firmware in the same way as the Dell card. Lastly, as pointed out, if you have an iMac 27" Mid 2011 with issues, the GPU is most likely the cause and Apple will fix it if it's no older than four years, because it's a recognized issue.Īpple refused to fix this one because it was sold in 2011 but if you want to fight Apple, maybe that'll work too - I chose to fix it myself instead. You can get a working card on Ebay or Aliexpress - any MXM 3.0 card pulled from an iMac should be fine.