[Simh] HSC vs UDA/QDA

[Bob Supnik]

The HSC family offered a superset of capabilities compared to the 
UDA50/QDA50. In particular,

- tape as well as disk support (TMSCP as well as MSCP);
- controller-based disk to tape backups and tape to disk restores;
- controller-based disk to disk duplication;
- controller-based volume shadowing (RAID 1).

UDA50/QDA50 did not support tape drives, disk duplication, or 
controller-based volume shadowing.

HSC supported some data caching; UDA50/QDA50 did not.

/Bob