The size of the AT VM(s) to which to deploy instances of your role. The size of the VM determines the number of CPU cores, ...

The size of the AT VM(s) to which to deploy instances of your role. 
The size of the VM determines the number of CPU cores, the memory capacity, and the local file system size allocated to a running instance.
Possible values are: Small (1 Core, 1.7GB RAM, 250GB Disk), Medium (2 Cores, 3.5GB RAM, 500GB Disk), 
Large (4 Cores, 7GB RAM, 1000 GB Disk), ExtraLarge (8 Cores, 14GB RAM, 2000 GB Disk).