On Sun, 12 Sep 2004, Ethan Dicks wrote:
> On Sun, Sep 12, 2004 at 02:29:16PM -0700, vrs wrote:
> > From: "Ethan Dicks" <dickset_at_amanda.spole.gov>
> > > There are approximately 1000 transistors in a PDP-8/S (plus lots of diodes
> > > and resistors and the core stack). Even with SMT, that's a lot of square
> > > footage.
> >
> > I'm not so sure it would be impossibly huge. If one imagined a transistor
> > and associated passives requiring a square 0.5" on a side, then a 16" square
> > board would have room for 32x32=1024 such elements. That seems large enough
> > to be really impressive (without being undisplayable).
> >
> > Or am I missing something?
>
> Turn the problem around - the PDP-8/S has a backplane that is approximately
> 16" x 30" with over 100 Flip Chips. If you were to attempt to turn that
> particular design into a single planar board of the same size, the contents
> of each Flip Chip would have to fit into the same square area as one back-
> plane slot (about 0.5" x 3.5"). I don't doubt that any of those circuits
> would fit in 2 sq in, that's for a 16"x30" board. Of course, a significant
> volume of the PDP-8/S is devoted to the core plane and core circuits, so
> perhaps it would fit in 16"x16". Just keep in mind how many square feet of
> thru-hole space is _in_ a PDP-8... SMT will reduce the amount of space
> required, but there is a lot of space to reduce.
>
> -ethan
>
Actually I doubt I would have trouble fitting most Flip Chips onto 1 sq inch
with not even very current SMT tech: 0603 resistors/caps, sc70
transistors/diodes.
Memory is a problem though. I wonder what is the simplest commercial
serial CPU ever made?
(kicking himself for giving away the PDP8-S that he had many years ago)
> --
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>
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>
Received on Sun Sep 12 2004 - 19:18:39 BST