I had forgotten about OrBit. According to this very nice document: http://xeroxalto.computerhistory.org/Indigo/Spruce/documents/.orbitguide.press!1.pdf
... the Orbit hardware was 4 cards in the Alto II backplane. As I recall, the SLOT interface was only 1 card; it was connected to a slower speed printer. The only modification to the Alto: wire wrapping the task signals (don't ask me how I know...) And yes, I agree, only the high bandwidth I/O used tasks. The use of tasks and "time sharing" the Alto processor innards is one of the Alto's real treats.
