> On Feb 24, 2021, at 7:06 PM, Noel Chiappa via cctalk <[email protected]>
> wrote:
>
>> From: Chris Zach
>
>> technically the MASSBUS cable is just an extension of the Unibus
>
> No.
>
> For one thing, the MASSBUS has no lines for carrying memory addresses. So
> there is no way to even build a box that 'translates' MASSBUS to UNIBUS; the
> semantics ('the things you can say', basically) of the two busses are so very
> different.
It's faintly true if you look at the Massbus adapter, rather than the cable.
But only faintly. There's a good reason why the big disks on many DEC machines
were Massbus devices until MSCP arrived. It's quite clear on Unibus PDP-11s,
which needed Massbus both for speed and for a cleaner answer to more-than-18
bit addressing.
paul
