[Simh] Multiple telnet ports in SimH to RSTS/E 9.6

[Clem Cole]

On Thu, Dec 31, 2015 at 3:40 PM, Paul Koning <paulkoning at comcast.net> wrote:

> DH/DHV/DHU have DMA output which means fewer interrupts.  On a real PDP11
> with very high output demands, that can make a clear difference.

​This is an understatement.   More over real DH's supported a DM11 which
was full modem control, sadly the DZ had a half-way modem control.   The
designer (whom I will not mention by name) later messed up the original
modem control on the console of the MC-500.  It took a SW guy (i.e. me) to
teach him how why all of the wires are needed.​

The downside of the original DH was that was a "full system unit" -- its
was SSI/MSI TTL with the only LSI part being the Western Digital UART.
Actually a very impressive design, but expensive to manufacture.  The DZ
was designed to replace it begin 8 lines per single board - so you got the
same # of serial ports (16) in two slots, as opposed to entire system unit
- but the system interface sucked and you lost modem control.


> ​....
>   But for most applications you're not likely to notice, and that's
> especially true in emulation.

​Can't speak for RSTS or RSX but for UNIX it makes a >>huge<< difference.
In fact Ken O of Able Computer made the definitive DH not DEC.  His product
was called the DHDM which was a single board with 16 lines and full modem
control, could run all the DEC diagnostics and actually was a little
smarter than the DEC implementation as he supported HW flow control which
the original did not.​

​   Many (most) serious UNIX systems with his product, particularly when
you attached things like "trailblazer" modem to yours system at 38K or
more.   A single DHDM with full modem control, cost the same as a single 8
line DZ; so it was a no brainer from a purchasing stand point.

Although in defense of Paul, being inside DEC at the time, was probably
hard to get the Able product; although I think I remember aps saying he had
get a couple for decvax because the DZ load was killing them (aps I think
you read this - do you remember/care to comment??).

Which brings me a question for Mark and Bob?   IIRC simh does not support
the DH, only the DZ.   I think I saw there was support for one of the QBUS
DH's but not the real thing.  If that's true, how hard would it be to make
it support the regular DH?

​Clem​





​*** ​
Ken
​ ​
is someone
 I will add to Warren's UNIX people list at some point
​.  BTW: At one point I got him to make a really cool product - which I
think I have seen Noel also refer and ask about -- the Enable11 which was
an UNIBUS cache card with a MMU on it, which he and I collaborated on (my
first "published" paper - years ago).  Anyway it allowed you to get 22 bit
addressing on an 11/40 class system - did not solve the I/D issue, but was
a major help for 11/34A systems (again adding that to simH would might make
some sense.  2.xBSD will recognize it on boot and use it).

​    As another side note, the DHDM was his biggest seller and a couple of
years later, I also tried to get him to make a DHDM like card for the PC.
At the time, he said that he could not figure out how to make money at it
because add-in cards on the PC bus were so cheap.  Eventually the Rocket
Port guys did something similar with a custom ASIC and that became the
serial solution for PC UNIX systems (I think I still have one in my
collection of old stuff in the basement).​
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