11 Dec
2021
11 Dec
'21
1:08 a.m.
Those names almost sound like they want to be familiar, but not quite.?
What I recall for a DN20 was that, in terms of communication, MCB only
had two speeds.
* A 'fast' interface could do 56 KBid, synchronous.? I /think/ that
part was called a "KMC".? It may have had some sort of embedded
microprocessor on it, but I don't recall what kind of operations it
performed.
* A 'slow' interface could do up to 9.6 KBid (I think).? I can't quite
remember what it was called.? Maybe a DUP-11?? I might be getting
that mixed up with the RSX20F front end, which had single line
interfaces that I think were called DL's.
I don't recall that MCB could do asynchronous communications, but I
don't remember that it did.? I can't remember how we connected distant
systems (CMU, Case Western and Stevens) when we were first building
CCnet.? I had thought that we were using synchronous modems, but I
wouldn't swear to it.
There was a bit of an argument when we finally got Ethernet (and the CI)
and DECnet IV that most of the DN20's should be disconnected and
removed,? This was to free up space in our perennially cramped machine
room, but it would have meant less heat, electricity and maybe less
maintenance $$$.? The overall head of Tops-20 systems programming
decided to play it conservatively and keep them, 'just in case'.? I
think if DEC had not walked away from the 36 bit market, they probably
would have eventually been pitched.
We had a Pro, but this was largely to port Kermit to it.? I think
Stevens went with Pro's in a rather large way, but I don't remember what
they ran.
------------------------------------------------------------------------
On 12/10/21 3:36 PM, Paul Koning wrote:
The mainstream comm link before Ethernet was the DMC-11 or DMR-11. Async DDCMP is a low
cost alternative (with lower performance). You'd tend to find it in embedded
applications, which is why it's a key part of RSX. And it appears in devices like the
VT71 typesetting terminal.
RSTS/E did not do async DDCMP for a long time; I added it at some point to get DECnet
onto the Pro. That was unofficial; in V10.1 it became part of the regular release but
even there it is a bit clunky and not quite complete. But it's enough that you can
get DECnet/E to use a terminal line.
paul
> ------------------------------------------------------------------------
> On Dec 10, 2021, at 3:29 PM, Thomas DeBellis<tommytimesharing at gmail.com>
wrote:
>
> I know VMS at least did some kind of line. Columbia's chemistry department got a
VAX before the campus Ethernet existed, so that wouldn't have been an option.
>
> However, I can't remember whether it was a synchronous or asynchronous
connection; only that the 'wire' went into one of our DN20's (I think CU20B).
I think the 'wire' had modems on both sides, but I can't remember what those
were, either.