> On Feb 24, 2021, at 9:06 AM, Chris Zach via cctalk <cctalk@classiccmp.org>
> wrote:
>
>> I happen to have a massbus adapter and the cabling with terminator for my
>> 11/750, but I never came across any massbus peripherals. Considering the
>> price back then and the size for these, they seem nowadays quite rare, which
>> is a real pity.
>
> Sort of. MASSBUS was a very overpriced and to be honest weird system that DEC
> developed in an attempt to be like IBM and charge very high markups for
> generic peripherals. While it did support a variety of interface formats (I
> don't think the RS03 and 04 were SMD, and I know the RP07 was *not* SMD) the
> industry quickly centered on SMD and that was that.
Overpriced? Compared to what? SMD didn't appear until later; I know Massbus
existed in 1974, perhaps earlier. What else would do the job back then?
> 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.
Electrically it works. I believe at least one system/OS supports this; TOPS-10
perhaps? But most operating systems do not, and yes, that would be a driver
issue.
Similarly, not all OS support RS03/04 and RM/RP on the same Massbus (RSTS
doesn't for example).
Meanwhile, speaking of the RP07: DEC never supported that on any PDP-11, but it
actually works just fine on the high performance Massbus of the 11/70. In the
RSTS group we had one on the big 11/70 system ("ARK" because at one point it
had "two of everything"). So RSTS/E will happily drive such a device, if you
can manage to power it up.
>> ...
>
> (Yes, I did use a MASSBUS cable to tow a car once. Worked fine)
:-) I think IBM's "bus and tag" 360 channel cables are even thicker than a
Massbus cable.
> I still have an RM80 drive in my house here, I fire it up every 5 years or
> so. Mostly for when I get my Decsystem/20 back together.
>
> It has the RM80 personality module which is the difference between the R80
> and RM80. To be honest I'd bet that one could put an RA81 personality module
> into it and make an RA80 drive....
>
> Far more interesting would be to see if one could put the RM80 personality
> module into an RA81 drive and turn that into a 456mb MASSBUS drive. THAT
> would be interesting....
Yes, but you'd need some driver work, since Massbus disk drivers have to deal
with the actual drive topology. So you'd have to define a Massbus ID value for
"RM81" and pick the appropriate sector/head/cylinder count. Depending on the
OS this may be fairly easy or not so easy. I know how to do it in RSTS (at the
source level -- doing it by patches might also be doable).
paul
