I'm not sure if this applies to the SB180 with COMM180, but the doc with the SB180FX states:
8. You may now operate your system in either of two disk contexts. If you prefer floppy disks as your regular working media, the system defaults to this mode. Known as the floppy context, the floppies remain drives A: through D: and the hard disk is accessed as drives E: through H:.
It is recommended that you run the program to change the disk context with the 'H' option aná operate under the hard disk context. The command 'CDC E' swaps drive assignments between the hard disk and the floppies. The floppies are now mapped to drives E: through H: and the hard disk is mapped to drives A: through D:. (The highest drive letter allowable is dependent on the number of floppies you have and the number of partitions you've defined.)