I wrote:
> Actually, DEC used over-the-edge cabling on an early minicomputer, and
> abandoned it because it was LESS reliable than backplane connection,
> and also made the machines much harder to service.
>
> Reference: _Computer Engineering: A DEC View of Hardware Systems Design_
Bill Pechter <pechter_at_pechter.dyndns.org> wrote:
> A great book... but wrong on this one.
>
> The hp stuff had one over the edge interconnect cable of less than 10
> inches.
>
> The DEC 11/40 (45,50,55,70, etc) in the BA11-F cabinet (the worst
> offender) had about 1/3 to 3/4 of an inch of ribbon cables (thickness)
> running through the cable trough an often popping off the Berg connector
> at the top of the Hex, Quad or Dual board (most had no locking ears on
> the connector. Yup, the backplane is more reliable as over the top
> connectors, but between board cables (RH11, RH70, Cache, etc) were my
> biggest pain in the _at_#$%^ at DEC). The 11/780 was a lot better with the
> exception of the lousy SBI cables that were failure prone and a bitch to
> troubleshoot.
I'm not talking about I/O cables that are many feet long between a card and
an external device, nor cables under two inches between just a few boards
in the same backplane.
I'm talking about using over-the-edge cabling for bussing signals between
many cards in the same backplane, and that's what I was referring to the
book about. This was done in the PDP-6, IIRC, and they decided that it
was a maintenance nightmare. If HP somehow made this scheme work reliably
and somehow kept it from being a headache to troubleshoot, I'd be interested
in hearing how they did it. Obviously HP must not have thought it was
a particularly great technique, since they generally aren't using it today.
Received on Mon Nov 22 1999 - 18:30:46 GMT