7 Apr
2013
7 Apr
'13
5:20 p.m.
On Fri, 5 Apr 2013, Paul_Koning at Dell.com wrote:
On Apr 4, 2013, at 6:44 PM, Clem Cole wrote:
...
But that's for terminals up to 9600 baud. For networking, you'd use a DMC-11
unless your OS supported the cheaper devices and money was that tight -- that one goes
back to about 1976 and delivers up to 1 Mb/s depending on model (up to 56 kB/s long haul,
given suitable modems).
Hmm - are the DMC and DMR that old? I remember fighting the firmware in the them to
allow high speed serial networking. They had a dedicated microprocessor on them (8080A
or 8085 IIRC - but it may have been something custom). They were expensive, which why
Berk-NET used 9600 baud serial lines, until we got 3COM & Interlan Ethernet cards at
Berkeley in 1983.
My 1976 Peripherals Handbook has a description of the DMC-11 in it. And I also remember
it was used in Typeset-11, which had a custom network implementation specific to it that
included Phase III style routing back in 1978. (No relationship to DECnet at all either
in architecture or implementation.)
A DMC-11 is essentially a KMC-11 with programming fixed in ROM, rather than dowloadable in
RAM, plus a line card. The KMC-11 processor is a custom engine, its instruction set
looks somewhat like microcode. No connection to any Intel chips, that couldn't
possibly have come within a mile of the performance requirements. Come to think of it,
the first use of a 808x series chip in DEC products I can think of is the head servo
control processor in the RA80. There may have been 8031s in some other spots, I no
longer remember where I saw those.
...
But I do remember our college main timesharing system, in 1973, a PDP-11/20 with 28 kW of
memory, RSTS V4A, and 16 terminals on 16 separate KL11 or DL11 interfaces. Oh yes, and a
mean time between crashes of about 1 day.
Are you sure it was a 11/20, not an 11/40? I did not think RSTS could run without the
MMU. With 16 DL/KL11's even with an 11/40 the interrupt rate had to been
wretched.
Positive. It was RSTS V4A-12, which did not use an MMU and required only 28 kW of memory
(24 kW for a minimal install). RSTS started requiring an MMU in version 5, the first
version that was called RSTS/E (for "Extended" as in extended memory).
And yes, a box full of single line serial cards. Most of them ran at 110 Baud driving
ASR33s; one or two were talking to TI Silent 700 terminals (300 baud printing on thermal
paper), and one was feeding a Beehive editing terminal, don't remember what speed,
almost certainly no higher than 1200 Baud because it was about 1000 feet from the
computer. All this on 20 mA current loop connections, no RS232 as far as I remember.
(The Beehive was for the London Stage project, an amazingly complex project to digitize
and index a large body of historical reference books, back when OCR didn't really
exist yet. There's a neat book about it, "Travels in Computerland" by the
project director prof. Ben Schneider.)
Also an RK05 for system disk, an RF11 swap disk, and some DECtapes for additional file
storage in case you wanted to save more stuff than could fit on the "large disk"
(i.e., the RK05).
Because of the reliability issues, we had a long battle with DEC to get it fixed. The
actual root cause may have been interference from the nearby campus FM broadcast
transmitter (3 kW around 90 MHz). But whatever it was, we never got a real fix for that;
eventually DEC threw in the towel and delivered a "replacement part" -- an 11/45
with a pile of new peripherals and a RSTS/E kit. :-) That did the job.
paul
Our 11/20 (also running RSTS V4A-12) ran for years with only 1 LA36 tied to it. There
were 2 DL11's in the chassis (not hooked to anything) and 2 old ASR33's in the
basement, but it was obvious these had not been hooked up in years. It was strange to
inherit a machine that had a multitasking, multiuser operating system on it, with only 1
terminal (running 300 baud). The math professor that had been in charge of it was leaving
and needed someone to take command of this fine old machine. We couldn't wait until
he FINALLY gave us the system 1,2 account password which was: SECRET
Yes, it had never been changed, and he had never run a sysgen. And unlike
Paul's experience, I don't think this machine ever crashed. When we did finally
appropriate the funds to purchase 2 VT55 terminals and hooked the DL11's to them, it
was like watching paint dry, waiting for the screen to update at 300 baud. My Elmer
found some information on installing larger capacitors and a different pot that would
allow us to run 2400 baud. This was quite a chore as we were supposed to be able to dial
it all in with an oscilloscope (that never did get it to work). Eventually, I wrote a
small display loop that was directed at that DL11 and we manually turned the pot while it
was running until the gibberish turned into something readable. The large caps on the
DL11's held the cards in the BA11 at strange angles and we always thought they would
short together, but somehow, it all ran.
Our original disk drives were the Diablo RK03's which were not very reliable (we
couldn't wait to upgrade to 3 RK05's). That extra RK05 with an additional 2.5
meg made all the difference in the world. ;-)
Brett