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It doesn’t quite work :) , a little bit, but not really.

Often if the specifications of computers match with other Macs you can install an older OS X on it then what came pre-installed on the Mac. Like in this situation I discovered that the Macbook Pro Early 2011 (MacBookPro8,1) has a lot of specifications in common with the Mac Mini Mid 2011 (MacMini5,1)

Same CPU, GPU and ram type. Both have Thunderbolt, bluetooth, wifi, Sata 2 clocked at higher speeds etc.

The Macbook comes with Snow Leopard 10.6.6 and the Mac mini with Lion 10.7. In the old days that would mean that the Mac mini could also run 10.6.6 or newer (10.6.8). Because all drivers are available. Thus if Lion or Mountain Lion doesn’t work for you, you could downgrade to Snow Leopard.

I’ve tried this many times before with G5 macs, earlier Intel models and all kinds of hardware really.

But in this case it seems Apple used a different I/O chip in the Mac mini. Also the I/O for the thunderbolt seems different. Because of these tiny hardware differences it doesn’t work. Very sneaky.

I successfully installed Snow Leopard on the Mac Mini but quickly discovered that the Sata Bus had a throughput of maybe 10/20 kilobytes while using the system. Instead of the advertised 3 Gigabit. This basically means the Sata Bus functions in a sort of fallback mode called PIO. And this is something of the 80′s and with that is super slow. Copying data and writing to the disk will literally take hours.

Another thing that seems to happen is that when you use the Thunderbolt port on the Mac Mini and Snow Leopard loads, the screen goes black. This suggests the firmware or the thunderbolt chip has a slight difference with the Macbook version of it. The Thunderbolt port does, however, keep showing as connected in System information. But it has no output.

However, and this is the weird part. Sata and Thunderbolt worked fine throughout the installation of the setup. This suggests this can be resolved with a driver or modification in Snow Leopard somewhere but I couldn’t find anything constructive for this. I guess no-one has tried this before. Since such things are notoriously hard to find for OS X I didn’t go into that much further and simply upgraded to Mountain Lion.