Ok, I have a bit of a challenge here.... My 80 year old dad is used to using 10.6 (snow leopard), and does not want to upgrade. Recently his 2006 Imac died, so I purchased for him the last Imac that natively runs Snow Leopard (a mid 2011 Imac). Now the problem... It came with High Sierra installed on it. I have a retail copy of 10.6, but the computer won't boot that. So I am going to contact apple tomorrow and order a copy of the original recovery DVD for the machine. In the course of doing my research on this, I found out that several EFI upgrades have been pushed since 10.6, and I am wondering if they will prevent me from installing from the recover DVD. Does anyone have any experience trying to do this?