Command-based or FIS-based Host Support
A SATA PM requires that controllers support either command-based switching or FIS (Frame Information Structure)-based switching in order to use port multiplication. Each paradigm offers unique capabilities suited for particular environments.
Command-based switching, conceptually similar to a mechanical A/B switch, limits the host to issue commands to only one drive at a time. Commands to other drives will not be issued until the command queue is completed for the prior transaction. Since command-based switching only accesses one drive at a time, it does not take advantage of the potentially higher speed host link. Therefore, command-based switching is ideal for simple drive expansion where capacity is more important than performance.