Dzogchen is basically the same as Maha Ati. its just the same word in Sanskrit. Sanskrit is an Indian language- which is where the Tibetan's got all their texts from. In one famous episode when two monks were bringing books from Indian by boat, one monk saw the others material was good, so rocked the boat causing his rivals library to fall into the water-the lake or river or whatever. There are several schools of Tibetan Buddhism, but the Nyingmapa or Old Translation School is mostly connected with Dzogchen. The Dalai Lama's school the Gelugpa took over Tibet in the 16th C when everything became corrupt & they did not like it very much considering it as a form of black magic. The present Dalai-lama however in keeping with his policy of making Tibet's culture an overall system of knowledge did receive some teachings but he is the first Dalai Lama to do so. The Nyingma tradition divides Buddha's teachings into nine vehicles with ati as the 9th very pinnacle-indeed it means 'above all else.' It is difficult to describe but one analogy is that of a laxative-if the more run of the mill Buddhism is like taking a senna tablet or bisacodyl then maha-ati is like taking elephant dope or the sky falling on your head like: 'a huge blue pancake.' Not sure what they mean by that but the point I'm trying to make is gentle it is not. If you want to tune into the Buddhist equivalent of an H bomb then this is your baby. Unlike the other schools which you can get from books you need an ati-master to give you transmission of this secret. They don't like doing this unless pushed & there are many stories so related. Dzogchen adherents look pretty normal which is why the Chinese didn't find them all when they took over. One that died was a road-maker-they only knew he was a dzogchen master when he died & his body shrunk to half it's size:-a sign of great realization!