[HECnet] VAX/VMS 1.50

[Paul_Koning at Dell.com]

On Apr 4, 2013, at 6:44 PM, Clem Cole wrote:

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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.

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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