Since DEC was sold to Compaq, the bottom has fairly well dropped out of the
PDP-11 spares market. This is true of both resale value and availability.
Nobody wants to stock a part for 5 years, then have it bring only $100 because the
purchaser said, "$1200? Forget it. We'll go to an Intel solution instead."
The Current PDP-11 Situation
Like RSX consulting, once you could buy PDP-11 hardware on
every corner. The DEC Professional, VAX Professional,
and Hardcopy listed dozens of add-on sellers, and dozens more
DEC resellers.
That was then. This is now. Since 1990 almost everyone has
dropped out of the field. UNIBUS hardware is no longer made, and now
boards are like gold ... the very same boards that people were throwing
away 15 years ago because they couldn't get postage value when trying
to resell them.
The Q-bus field is somewhat better, because many VAXes still supported
Q-bus hardware well into the mid- and late 1990s. Still, those options
used specifically for PDP-11s are becoming hard to find as spares.
We can be sure that the situation will not be any better in the future.
In 5 years, supporting PDP-11s will be like trying to support PDP-8s
today. Here are a few comments on the hardware situation.
Buying Systems
For a long time, the simplest way to pick up systems if you weren't
particular about the exact model, was to watch the vmsnet.pdp-11
newsgroup. Not any more. From time to time, something still turns
up, but you have to be prepared to drive cross-country on short notice,
most of the time it's not something you want, and even if it is what you
want, you may have to tear down and take home an entire system.
If you want 11/34s, that's fine, but nobody is giving
away 11/94s with Unibus SCSI adapters.
Over the last 10 years, all the system integrators have gone away. Now
you need to find someone who worked with PDP-11s in the glory days, someone
who knew PDP-11s well because the knowledge decays fast when not
used. And be willing to pay them well to integrate a new system.
From experiences over the last ten years, we've decided that there is only
one company left that can do a decent system integration of a "new" PDP-11.
They are Finite Systems, Ltd.,
based out of Shakopee, Minnesota. Talk to Dick Cecchini (sounds like
"zucchini") and tell him Machine Intelligence sent you. Then he won't
hang up or laugh at you.
Spare Parts
The spare parts situation is much the same as the systems situation. It's
a little bit better, though, because there are still some DEC resale houses
in the business with old PDP-11 parts on the shelf.
If you think you'll ever need spare parts, buy them now.
They won't get any cheaper in the future and when you need them, you'll need
them now. Why? Because the only PDP-11s still running, are running
because they're mission-critical systems. Not because they're lovely pieces
of hardware, but because they still do a critical job.
Before buying spares, talk to someone who still has the old DEC-O-LOG
microfiche, and ask them to look up the "current" (i.e., last) revision
level of the board. This is mandatory! You must do it every time
you buy a board. Out of revision boards turn up far too frequently on
the used market, and many of the last revisions are critical for the board
to work right. Example: The UDA50 before revision "K" did not do bad block
replacement correctly. You don't want to buy something that looks like it
works, but will stab you in the back in operation.
Where to buy spares ... well, really there are so few choices you'll have to
shop them all, and take the best price. Get a copy of The Processor
or Computer Hot Line and start making calls. Look on ebay®.
Those are about the only
options for spares. DEC / Compaq / HP is long out of the module business.
You'll have to shop the used market to get anything for PDP-11s at a halfway
reasonable price.
Selling Systems / Parts
Alas for anyone who wants to sell a complete PDP-11 system or parts.
In the early 1990s, people were stocking up on PDP-11 hardware because
they knew it would be harder to get in the future. Today, however,
everyone who needed those spare parts and systems already has them.
There is very little sale value to PDP-11 systems or hardware today, unless
the part in question is a specific, hard to get module such as an
ICS11 submodule. Processors, disk controllers, I/O cards, racks and
cabinets all sell on ebay® today for ten to forty dollars. This
is great for hobbyists who have time and the inclination to fiddle
with hardware of unknown provenance.
However, it also indicates that nobody in the used market is buying,
and that trying to make a
buck off that 11/34 in dead storage is no longer possible.
System Upgrades
If you have a need for a faster processor, ideally you should stick
with DEC-manufactured hardware. It all had quirks, but DEC was aware
of that and handled it in the operating systems.
The upgrade path for 11/23 (dual wide) is to the 11/73 (dual wide).
The upgrade path for 11/23 (quad wide) is to the 11/73 (quad wide).
The upgrade path for the 11/44 and 11/70 is to the 11/84 or 11/94.
The upgrade path for any old UNIBUS CPU (11/34, 11/40, etc.)
is to the 11/44.
The upgrade path for the 11/73 is to the 11/83 or 11/93.
The upgrade path for the 11/83 is to the 11/93.
The upgrade path for the 11/84 is to the 11/94.
And if you find yourself at the 11/93 or 11/94 and still need more
performance, you must leave the DEC world and look at third-party
system upgrades. At least one company offers a PDP-11 emulator that
runs on an Intel-based PC. However, running a high-reliability control
application in an emulator under Windows might well make
shivers of fear run up and down anyone's spine.
11/70 Performance Upgrades
In the mid- to late 1980s, SETASI / Digital Data Systems marketed a series
of enhancements for the 11/70. Called the PEP-70 and Hypercache, these
modules replaced the touchy, difficult to configure external MK11 memory boxes,
and gave the system a reasonable performance boost through CPU enhancements as well.
As time went on, the 11/70s fell from use and were replaced by 11/84s
and 11/94s with slightly higher performance and much better reliability.
While an 11/70 with the PEP-70 upgrades would still marginally outrun an 84 or
94 on disk I/O speed, (as anyone who
has ever worked on an 11/70 can verify) 11/70s were surly monsters to maintain.
There are not many 11/70s still in use anywhere in the
world. Those in use probably don't require the PEP-70
or Hypercache enhancements at this stage of their life.
This is a good thing, because the chances of finding:
-
A complete and working PEP-70 hardware set
-
With the necessary documents to install and configure it
-
The necessary software to test and validate it
-
And an engineer competent to work on an 11/70 CPU
are close to zero.
11/70 backplanes are now well over a quarter century old. They
were black-and-white spaghetti at best when new; now they are
fragile and oxidized to boot.
Only an extremely brave, but more likely foolish,
system owner would swap any CPU cards without dire need.
"Never touch a working 70 for anything
short of smoke coming out of it," was the credo of most
engineers who worked on them.
If you do have an 11/70 and require performance improvements,
from a reliability standpoint you are much better off to look at an 11/94
or splitting the application across two systems via shim routines and DECnet.
