resurrecting a PDP-11/10

From: Jerome H. Fine <>
Date: Fri Feb 28 08:47:00 2003

>Ethan Dicks wrote:

> --- Tony Duell <> wrote:
> > Serial pots were used for things other than terminals... Many printers
> > had serial interfaces, as did the TU58 (which is what started this
> > discussion).
> True, but serial terminals were not common when the PDP-11/10 was
> being sold new. In the DEC world, it was the day of ASR-33s and
> parallel line printers on the low end. Five years later, serial
> printers were much more common (LA-36 and newer).

Jerome Fine replies:

I am not sure exactly when the system I shall refer to was first installed,
but I arrived on the scene around 1979 after it had been running for
a few years.

I understand that the initial installation used a PDP-11/10 with a DZ11
to communicate with the field plus the usual single DL11 for the console
which was, if I remember correctly, a VT52.

The system ran RT-11 with 2 RK05 disk drives. I think that the first
version used was V2.0 something.

Later the production system was upgraded to a PDP-11/34A and
Multi-User Basic was added which ran in the Background while the
original program was run in the Foreground.

The DZ11 used all 16 channels to communicate with many other terminals
spread around the factory. The DZ11 was a great improvement over the
DL11 since it contained a SILO for incoming characters. Whereas the
DL11 would lose a character if the ISR (Interrupt Service Routine) did
not manage to handle the previous character quickly enough, the DZ11
was able to store up to 32 (or perhaps 64) characters in the SILO. In
addition, after each character was processed, the ISR was able to
determine if any characters remained in the SILO, so the overhead of
exiting and re-entering the ISR was avoided.

> > While timesharing was rare on machines without memory managemnt, it was
> > not uncommon to have 3 or 4 serial ports in such machines.
> Again, my experiences in the DEC world are that Unibus RT-11-class
> machines ( less than 28KW of RAM, one or two disk devices, no MMU )
> tended not to have multiple DL-11s. I'm not saying it never happened,
> it just wasn't common. It was much more common when the low end
> switched to the Qbus platforms.

Until about 1982, the 11/23 was the high end in the Qbus systems.
Is that what you meant?

> > Be warned that the DL11 (simple serial port) and the DZ11 (etc --
> > 'multiplexer' serial ports) look very different in software! Older OSes
> > may well only support the former.
> True. Good call. I have never used a DZ-11 under any version of
> RT-11 and have no idea how it would work out. I have used DZ-11s
> with RSTS and RSX. Works great.

I think that the DZ11 was first supported under RT-11 in V4.00, but
I can't be sure. That would have been at least by 1980. Certainly
by 1983 when V5.00 of RT-11 was released, I am almost certain.

The DZ11 could support up to 16 channels on the Unibus. On the
Qbus, the DZV11 could support ONLY 4 channels. As far as I
remember, the DZ11 and the DZV11 looked the same to RT-11.

The DHV11 was not supported by RT-11 until V5.06 in August 1992.
TSX-PLUS supported the DHV11 many years before that.

Sincerely yours,

Jerome Fine
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Received on Fri Feb 28 2003 - 08:47:00 GMT

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