Actually Dec would take the stuff on contract in the mid to late 80s.
They went hard on customer service retention and came up with a third party mauntenance plan on stuff like Emulex controllers, CDC976x drives... etc.

Not sure if the Able was in the plan. Had to do with diags and parts availability.

I have some personal experience in the area, but I don't know if I can post it...

Too many war stories before Dec lost the war for survival.

The view from field service was fascinating including non-mergers with AT&T around 1984 and almost an outsource of the Bell Labs data centers to DEC in. 1984.

Bill
Sent from pechter@gmail.com

-----Original Message-----
From: Dave Horsfall <dave@horsfall.org>
To: Computer Old Farts Followers <coff@tuhs.org>
Sent: Fri, 28 Feb 2020 16:58
Subject: Re: [COFF] 52-pin D-Sub?

On Fri, 28 Feb 2020, Clem Cole wrote:

> DZ-11 sucked... for a number of reasons, the SW issue being just part of
> them, but they were short pinned and really did not do modems well,
> particularly high-speed ones like the Trailblazer. As you said, you
> could make them work, but why bother?

We used ours for local terminals only; 8 DZ-11s on the 11/70 worked fine
(I don't recall how fast, but probably around 2400/4800). As I said, it
came down to the driver.

> Unix folks figure out the best idea was to use the Able DH/DM -
> cheaper, only one unibus slot for 16 ports (as opposed to 2 for the DZ),
> fully wired on the DB25 end, hardware flow control and just worked
> better in that is will DMA. What was not to love...

Sure, but then DEC Field Circus won't touch the box.

> FWIW: One of the guys behind DZ (who I will leave nameless) also
> screwed up the first serial port on the Masscomp MC/500 after he left
> DEC. I got there too late to fix it in the first version of the CPU
> board. So it was not fixed until I tore him a new one and educated him
> on how RS-232 actually worked (I was the first lead for the data com
> group as well as 1/2 the OS team). I never quite understood why HW
> folks often though of the serial port as '3-wires' -- sigh.

Heh heh :-) I don't think I've ever seen RS-232 used "properly" i.e.
implementing DSR/DTR or RTS/CTS for other than flow control etc, and using
the secondary pins as well.

-- Dave