S7-400H and S7-1500H

Hi All,

         Please find the attachment. 

        Will some body explain me following concept.

        1. S7-400H – Synchronous adjustment (interrupted)
        2. S7-1500H – Asynchronous adjustment (continuous)
 

        What are advantages and disadvantage one over other.

        I am aware one major advantage is synchronization and switch over time.

Thanks