is Sierra the highest OS version that can be hacked onto an early 2008 iMac?

[Lynxpro]

Thought I'd pop in and ask a 2 part question here about unsupported versions of OS X/macOS being hacked onto an Early 2008 iMac [8,1]...

So...

1. Is Sierra or High Sierra the highest unsupported OS that can be loaded onto such a beast?

and

2. Is RAM still stuck at 6GB reliably?

The last time I looked into upgrading beyond El Capitan on this beast, there was a concern about the internal WiFi and losing functionality due to the lack of a driver in Sierra/High Sierra/etc for it which would thus require permanent hardwire ethernet connection or getting inside the case and installing a newer WiFi card.

I remember the RAM issue being another concern and that 6GB [1 2GB stick, 1 4GB stick] in any situation would be the only stable option since El Capitan itself had been a good 2 OS upgrades beyond the last time an OS was stable using an unsupported 8GB [2 4GB sticks] configuration. As it stands, this sucker is still running on a lowly 4GB [2 2GB sticks]. I know... embarrassing. But that's what happens with a mortgage and child support!

 

[CatNoodles]

1. You can install up to Catalina, I believe the latest Catalina update released on Nov. 5 is supported by this DosDude1 installer. I have been using Mojave on an iMac 8,1, runs surprisingly well, no stuttering when I'm streaming YT or Facebook. Application startup can take a while, though. Use DosDude1 installer for either Mojave or Catalina. Make sure after installation that you apply the patches relevant to your model (iMac 8,1)! You can do that by clicking "macOS Post Install" after the installation is successful but before you reboot the iMac. That includes patches for Wi-Fi and camera if you need them to work.
2. I saw a considerable increase in performance from 4 GB to 6 GB. I would highly suggest you to up the RAM. You'll also see a great improvement if you swap HDD for SSD.

 

[MultiFinder17]

I have two early 2008 iMacs in my classroom that I use daily, both happily running Mojave with the patcher. As the prior poster mentioned, the two most solid things you can do for the performance of these machines is 6GB of RAM and an SSD. With these, my 20" 2.4GHz iMac runs like a champ, handling Safari, MS Office, YouTube, and general productivity.

 

[qoop]

I decided to stick with Sierra after trying later OS versions with my five 12 core Macs (3.06GHz). I had issues with my NVidia GTX680 (2.5GB reflashed) cards, USB3 cards (CalDigit & Sonnet) and several others. Some people have no issues at all with newer versions, it's pot luck sometimes.