Downgrade 2011 iMac per loaded with mountain lion back to lion or snow leopard?

Find it here (two specs of 2011 iMacs exist). Oldest version you can install is pre-installed Mac OSX.

aPple nErd said:

So basically, the ones preloaded with lion, I can downgrade to sl, but the Mtn lion ones can only be on mountain lion?

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That sounds likely: if a machine has only ever shipped with ML then any previous OS won't have platform drivers for that machine and won't be able to boot.