--- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> >
I kicked off this whole mess with...
> >
> > I have a chance to buy a 4kW core stack for the PDP-8/i (-8/L). It's
> > more than I want to pay, $100.
Then --- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
>
> Well, I've not bought core for a few years, and I payed a lot less than
> that.
Me, too.
> But I believe core is now soemthing of a collectable (alas by
> people who are not going to use it :-()
Sigh. :-P
> [...]
>
> > OTOH, I do have a broken (20-30 fractured cores) -8/L stack that I've
> > contemplated repairing. It's a parity stack, so I can scavenge wire
> > and cores from the parity plane (or just use the parity plane intact
> > as another bit, then use one pad of broken core to repair the other,
> > less damaged pad of broken core).
> What I would do :
>
> I'd buy the core at $100, since that way you do have the working 8K for
> your PDP. Then I'd try to mend the broken core plane that you already
> have. If you fail, well you still have a machine with 8K in it (you'd be
> kicking yourself, I think if you couldn't fix the old core and couldn't
> still get a replacement).
It seems the prudent thing to do, I was mostly just writhing about having
to pay double of what _I_ think it's worth. I was polling for a sanity
check to see if my expectations were unreasonable, or if the expectations
of those stick-it-on-a-bookshelf collectors were.
> If you do manage to mend it (and I think it's possible to re-string
> larger-sized cores by hand)
These are fairly large... much larger than on a 4kW stack for the PDP-11/20,
but that's a three-wire plane.
> then either make a 12K machine (if you can do that)...
Not inside the -8/i (massive backplane, room for CPU, EAE, 8kW core and
lots of I/O options. The -8/L expansion box _might_ take a total of 8kW)
> or sell one of the core units to another collector (and if $100 is
> the going rate you could probably get that for it). Or, of course, keep
> it as a spare.
I vote spare unless the price of core soars by one or two orders of
magnitude.
> > of time spent, it's cheaper for me to work a few hours and earn the money
> > that the core pirate wants; in terms of lessons learned, repairing a
> > 30-year-old core stack would be a big thrill, *if* it worked.
>
> Sure. Fixing old computers rarely makes financial sense, but then hobbies
> rarely do.
If I were in this for the money, I wouldn't be in it for the money. :-)
> But learning how to mend core memory is an interesting thing
> to learn to do IMHO (if I had a broken core unit you can bet I'd be
> trying to fix it...)
Do you have an opinion on how historically accurate is reasonable to
attempt? By this I mean that the parity plane (all by itself on a 3/4
empty PCB) has no damaged cores. If I move the sense/inhibit wires from
its slot on the paddle boards, I can borrow them intact to act as one of
the damaged bits, I can then disassemble the more damaged plane (or perhaps
the less damaged plane depending on where the damage is easier to get to)
and only have to repair _one_ plane.
In short: more like the original - disassemble the parity plane, removing
it from the stack, converting a 13-bit broken stack with 4 PCBs to a 12-bit
working stack, or, disassemble a broken plane, swap the data wires from it
to the parity plane, keeping all four PCBs inside the stack. The second
solution seems to make more sense from an effort and safety standpoint, the
first solution seems to me to be more "pure".
Thoughts?
-ethan
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Received on Mon Apr 19 1999 - 16:57:43 BST