How scarce (valuable) is core for the PDP-8? - test-drb@ccmp.vtda.org

19 Apr 1999

...
  When I mentioned the chance to buy a 4kW stack for the
PDP-8/i for $100...

 --- Lawrence LeMay &lt;lemay(a)cs.umn.edu&gt; responded:

  Actually, that's probably a reasonable price.

 Foo! 
Well, I didnt say that I would pay $100... Or that it was a great price.
But it might be a fair price.

Of course, If i didnt already have a bunch of core of various types, and
if i needed it to restore a pdp8 system (which would be at the 
absolute top of my list to do, as the first computer I ever saw, and
every used, was a PDP8/e) then I would probably pay it. And i'd be
cursing at whatever the past 20-30 years had done to make the board
not work anymore ;( And i'd probably try to locate Lassiter and see
if my some miracle he could repair the board, etc.

But, thats just me. To me, having a PDP8/e is the ultimate dream machine.
That, and having the room to store a PDP8/e...

-Lawrence LeMay

...

  Core memory boards, probably non-working, have
been going for a high price.   
 I got sniped for a PDP-11 double-core stack this weekend, backplane included,
 that went for $38, no reserve.

  Age and a nice visible setup increase the price. 

 The core stack for a PDP-8(i|L) is older than much of what's on the
 market, but none of the good stuff is visible at all on it.

  Now, I havent seen the memory in question. but
the pdp8/e core
 memory i've seen is all covered by a clear plastic shield. This
 increases its value as a display piece, as you can easily see
 all the core, and its all protected.  
 It's hard to describe the arrangement, but the core plane in question
 here is a block with two edge-connectors on either side, "dual-height"
 as they say, but it's much thicker - let's try bad ASCII art to illustrate...

   ########  ########
   xxxxxxxxxxxxxxxxxx == ######## ########
   ########  ########    ######## ########

   core planes            paddle-boards with wire harness

 The outside of the core plane part is covered in a "diode matrix", with
 a wad of twisted-pair wires that go off to paddle-boards, one for the
 sense bits, one for the inhibit bits.  The address lines come up the diode
 boards, the data comes up and down the paddle-boards. 

 There are several PCBs with core in the core stack, 4-bits per layer with
 an optional parity layer that has one pad of bits and three pads of core-less
 X-Y wires.  None of this is visible when the plane is assembled, and it's
 soldered together with lines of wires going up and down the planes. 

  Of course, in order to use the core on a pdp8/?
you would need
 a couple of support boards in addition to the core plane board
 itself. I would say that just the core plane, being of a nice
 size, and being very good 'visually' to display, and somewhat
 because its a PDP8 series board (nostalgia value), that its
 probably worth $100 all by itself. If it comes with the 2 support
 boards and the top connector things at that price, then i'd say
 its a bargain.  
 You are thinking of newer hardware.  The pre-OMNIBUS 8's have a wad of
 individual, single-height cards that contain the sense-amps and the inhibit
 drivers.  I have a pile of them from an -8/L that someone else had already
 begun to strip for parts before I bought it (it also happens to contain the
 only DEC lock that does *not* use the XX2247 key).  I'm not worried about
 the analog stuff... I need the core.

 Of course, as Allison pointed out, I could always stick in a lump of battery-
 backed static RAM.  I was contemplating building a wiring harness to adapt
 an RX8E on the back of either an -8/L (which has 8kW of core out of 12kW in
 an expansion cabinet) or on the -8/i.  I would use berg connector pins to
 stick the wires on the back side of the backplane (to avoid soldering, of
 course; but worst case, I just wire-wrap on a connector or two and use
 sheilded ribbon to move the signals around.

 The joys of restoration in a market of scarcity. :-P

 -ethan