Subject: PDP-8 *core* memory wanted

From: [email-masked] (Steve Hand)
Date: Mon, 9 Aug 1993 13:19:31 GMT

Do you have an unused PDP-8 *core* memory card (not solid-state) you
would be willing to sell cheaply?  I'd love to have a keepsake from
the days back in school when I programmed PDP-8's for a chemistry lab
(they controlled the X-ray diffractometers).  I'd prefer one where
you can see the little magnetic doughnuts...

Please respond via e-mail...

Thanks,
Steve
--
   . . .      Steven Hand   [email-masked]   mcnc!rti!sas!sassth
 .   _  \     SAS Institute Inc.,  SAS Campus Drive,  Cary, NC 27513    |
    / \  |  .   (919) 677-8000 ext. 6936 (work)   467-0295 (home)     \ | /
.  | (*) |        Not officially representing SAS Institute Inc.     --=*=--
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    \. . .         and sings it to me when my memory fails me.          |

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From: jones@pyrite (Douglas W. Jones,201H MLH,3193350740,3193382879)
Date: Mon, 9 Aug 1993 19:53:55 GMT

>From article <[email-masked]>, by [email-masked] (Steve Hand):
> 
> would be willing to sell cheaply?

If I find an irreparably broken board, I'll let people know, but those
of us trying to restore old PDP-8 systems to working order generally
want to keep what core we have in working order so we can put programs
in it!

> (they controlled the X-ray diffractometers).

You'd enjoy knowing that the U of Iowa has two PDP-8/I controlled X-ray
diffractometers sitting in mothballs right now!  They aren't surplus,
yet.

> I'd prefer one where you can see the little magnetic doughnuts...

Then you want an old core board, and not one of the new-fangled
(post 1970) ones!  The core DEC used in the 1970's was so tightly
packed with such small cores that it looked like a black fabric of
some kind.  If you looked real close, you could see the herring-bone
pattern of the cores, though.

				Doug Jones
				[email-masked]

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From: [email-masked] (Charles Lasner)
Date: 10 Aug 1993 04:00:55 GMT

>you can see the little magnetic doughnuts...

What's an *unused* PDP-8?

Some of us have objected that the so-called Computer Museum in Boston is
selling off its "artifacts" as it provides less of a look at the past of
computing and more into the commercialistic side of running a business.  There
have been several reports of machines no longer displayed that formerly were
not only displayed, but running, and (shudder!) rumors of machines with the
insides gutted, and replaced with video screens simulating what the real
machines may have looked like, or at least an unreasonable facsimile acceptable
to an unknowledgeable public.  The parts of PDP-8's and other machines wind up
as trivial souvenirs of the visit sold at nominal prices at the place of
business, etc.  I wonder how many of us old-computer fans are unable to produce
a specific result merely because they have sold off the last of some obscure
module, etc.

There are a lot of R-series modules that are pretty common admittedly, and it's
pretty easy to repair such a simple card, requiring essentially only a supply
of diodes and transistors.  (An exception is the variant that only uses the
FLIP-CHIP hybrid because they do occasionally fail, and these variant boards
cannot "neatly" take the original passive components they replace as do the
older boards.  However, kludges have been constructed that can be used to
replace the FLIP-CHIP in a pinch.  Also, some boards with the dual etch have
been cannibalized of FLIP-CHIP's to bail out a board that cannot have the
separated diodes and capacitors, and in their place loose components have
been installed, thus regaining the use of both modules.)

But there are quite rare cards that are needed for various machine functions.

A case in point is the R212.  This module is needed in groups of six to 
implement either the LINC-8 "Z" register or the MQ of the EAE option of either
the LINC-8 or PDP-8.  Thus, a LINC-8 cannot be complete without at least six
R212's and would want an optional six more.  Not too many PDP-8's were ever
made with EAE, and only about 150 LINC-8's were ever produced, so the total
known population of these cards is quite small (even when including DEC's
likely original spares count).

Another one is the B684, which is needed to drive the PDP-8 Memory buss
when a LINC-8 or PDP-8 gets more than 4K.  Twelve such cards are needed.  The
module may also have other applications, such as in the KA-10.

Perhaps we should make up an "endangered species" list for DEC modules for
our machines, where a rarity quotient is calculated for these cards, and thus
it becomes possible to "rate" their relative worth, etc., and perhaps can come
up with a trader's equity rating or somesuch.  This way would-be trades can be
established to allow everyone an opportunity to upgrade the machine of their
choice.  (I myself have a plethora of certain cards that very well might be
rare in general, and might want to trade for something else, or sell them, 
etc.)

Perhaps someone should contact the museum itself, since likely they would be
interested in someone trading expertise for hardware.  That would be more
"profitable" to them than getting incidental money selling PDP-8 parts as
"trinkets" to non-serious non-collectors who are merely casual visitors of the
museum.  Depending on what was salvaged, this may allow them to not alienate
groups such as our readership here, etc.

cjl