Questions about the Common Berthing Modules on the ISS. (Not about Commodore Business Machines)
The ISS has several different types of docking connectors. The CBM is the largest diameter, used to connect modules on the US Segment of the station. Unmanned cargo vehicles (HTV, Cygnus, Dragon) use the CBM port on the nadir (earth facing) side of the Harmony (Node 2) module for berthing.
Manned US craft (previous: Space Shuttle and future: DragonRider, Dream Chaser, CST-100, Orion) are meant to use the PMA (Pressurized Mating Adapaters).