Massbus - was: Re: VAX 11/750

Eric Smith spacewar at
Thu Feb 25 01:40:33 CST 2021

On Wed, Feb 24, 2021 at 7:06 AM Chris Zach via cctalk <cctalk at>

> Yes, the TM02 and TM03 formatters allowed MASSBUS to connect to Pertec
> drives, but I don't think you could run a tape drive and a disk drive on
> the same MASSBUS channel anyway. Wonder why, technically the MASSBUS
> cable is just an extension of the Unibus, so it shouldn't matter much
> what combination of cables you used. Maybe they just wrote different
> drivers or something.

There's nothing in the hardware that prevents it from being done, but DEC
OSes don't support it, and it's generally not a good idea. Tape activity
would block disk activity, because it doesn't have anything like modern
"tagged command queuing".

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