Installing OSX 10.8 on a Mac Mini2,1

I wanted to be able to build and test oaCapture on different OSX releases, but only Snow Leopard and Lion would install on my old Mac Mini. ¬†It would have been very convenient for me if I could also have tried Mountain Lion, but the installer just stopped at boot time with a “not allowed” icon ūüôĀ ¬†There’s no major reason the install shouldn’t work as far as I can find out. ¬†The later versions of OSX don’t have the proper driver for the video card, but for just testing that software would build and run that didn’t bother me too much.

After grubbing around on Google for some time trying to find the right thing to search for, I discovered two useful things:

  1. the OS installation contains a file listing all the hardware that Apple wants the OS to run on, and
  2. it is possible to boot a Mac into what’s called “Target Disk Mode” by pressing the “T” key on the keyboard when it boots. ¬†This makes the machine behave as an external disk connected by FireWire (or Thunderbolt, presumably).

The file listing the “compatible” hardware is¬†/System/Library/CoreServices/PlatformSupport.plist. ¬†It contains lists of the board ids and hardware types allowed. ¬†Hardware type in my case was fairly obvious as “macmini2,1”, but the board id was more troublesome until I discovered that this command, run in a terminal window, would give it to me:

ioreg -l | grep board-id | cut -d\" -f4

So, I noted that down and dug out a FireWire cable, connected the Mini up to another (later model) Mac, powered on the Mini (holding the T key down) and waited.  Shortly it displayed a large bouncing FireWire symbol on the console, at which point I put in the install media for Mountain Lion and booted the second machine.  From that point on everything worked as a normal installation.  I just had to select the FireWire disk as the place to install the OS, which the installer was quite happy to do.

Finally I opened a terminal window, edited /System/Library/CoreServices/PlatformSupport.plist and added my board id at the end of the “SupportedBoardIds” section and “macmini2,1” at the end of the “SupportedModelProperties” section. Then I shut down the newer Mac, powered off the Mini (in that order), unplugged the FireWire cable and rebooted the Mini, which happily started in Mountain Lion. The display was a bit ugly given the lack of a suitable driver, but I decided I could probably live with that.

By sheer chance however I happened to come across a set of rebuilt 64-bit GMA950 drivers that were claimed to work with Mountain Lion, packaged up as “3624-Kexts”. I downloaded them and in the knowledge that I could now re-install the OS should anything go horribly wrong, unzipped the file and dropped the Kext files, the bundles and plugins into the /System/Library/Extensions. One more reboot and I had a properly functioning display as well.

Now it’s done I don’t use the OS for much other than testing or checking out bugs, but for that purpose it’s been exceptionally useful.

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