'100' = '100-A' (system module 70-19974-00, PSU H7842-A, 24 K ROM)
'100+' = '100-B' (system module 70-1994-02, PSU H7842-D, 32 K ROM)
Once upon a time there was a 'Winchester Upgrade Kit' for the '-A'. Could explain the '+' sign.
Question: are the alternate interrupts (above) implemented in our driver?
