They are only connected via pressurized mating adapters. In fact it's not uncommon to move the modules around which they are in the process of doing now.

The russian orbital segment handles Guidance, Navigation & Control for the entire Station. This is the "hub" I spoke of replacing. It is only a small part of the station. It is 5 small segments.

The US Orbital Segment consists of 11 segments, all external fixtures, and the recently installed engines. This segment is controlled by mission controls in countries that supplied the modules.

Yes this means each module has its own controls.

The iss is a third generation modular station. Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

It is literally want to be able to take back apart.

It's also important to note the Russian and U.S. side have their own little de support systems. The Russians use the elektron system and the U.S. uses SFOG.

The Russian side uses 28v power, the us side uses 180v. The Russian Orbital Segment communicates directly with the ground via the Lira antenna mounted to Zvezda. The US Orbital Segment (USOS) makes use of two separate radio links mounted in the Z1 truss structure: the S band (used for audio) and Ku band (used for audio, video and data) systems.

Also, I actually got the idea from the Russians.

According to a 2009 report, Space Corporation Energia is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the Orbital Piloted Assembly and Experiment Complex (OPSEK).