25 Feb
2021
25 Feb
'21
11:06 a.m.
In answer to my own question: No it does not based on a bit of review.
Looks like unique cards to the 11/70.
C
On 2/25/2021 1:43 PM, Chris Zach via cctalk wrote:
Oh this is fun stuff. Is there a specification
write-up anywhere on the
MASSBUS overall?
For example I wonder if the RH70 could do a transfer >128kb at a time.
Another is around the RH11: There were two models, the traditional RH11
(which could only do so many words on a DMA transfer) and the RH11-C
which could do more words per transaction by basically running the
Unibus in "Hog mode". That allowed the 2020 to run RM03's at a full 3600
RPM (and I assume can allow the 2020 to run things like RM80's).
Another item I always wondered about was the RH11's support of two
unibuses. I think the idea was to do the data transfers on the second
bus right to an 11/45's FASTBUS memory without worrying about DMA
timeouts while running the control and status registers on the normal
UNIBUS (which wouldn't block other devices). I wonder, does the MBA on
an 11/70 use similar cards to an RH11?
C
On 2/25/2021 1:30 PM, Noel Chiappa via cctalk wrote:
> ???? > From: Paul Koning
>
> ???? > 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.
>
> I follow the first sentence, but I'm confused by the second,
> especially "a
> cleaner answer to more-than-18 bit addressing". The UNIBUS MASSBUS
> controller/adapter, the RH11, only has 18-bit addressing on the main
> memory
> side. It does have more than 18-bit addressing on the device side, but
> so does
> the RP11 (sort of). Are you thinking of the RH70? That does have
> access to
> more than 2^18 bytes of main memory, but that's because it connects to
> the
> -11/70 memory bus (as well as the UNIBUS, which is only used for
> control, not
> data).
>
> Similar questions about the speed point; passing data through an RH11
> doesn't
> increase the speed of the UNIBUS? Yes, the RH70 is faster, but that's
> because
> of its connection to the -11/70 memory bus.
>
> ??? Noel
>