Are SDS drills metric, standard or all the same?
There are three different SDS sizes: SDS plus, SDS top and SDS max.  You must match your tool type to the bits.  Within a given tool type (SDS plus, say), the tool side is the same.

They are available in both inch and metric sizes (on the cutting end). 

Wikipedia article on SDS shanks  

SDS-plus, SDS-Top and SDS-max. respectively: