[Matterwave]

Well I think that a physical computer is one that you would use. An abstract computer is like something that technically computes but wouldn't be usually considered a computer (e.g. a roll of tape on which you can write consecutive bits, or a bunch of stones arranged to store information). An open computer would be one which is connected to the internet or another machine. A closed computer would be one which is not connected to anything else.

This would be my guess at what those 4 types are...but I'm not sure either...