[ih] Arpanet physical connectors

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Jul 23 08:53:27 PDT 2020

    > From: Alex McKenzie

    > As mentioned in another post, BBN supplied the cable and specified the
    > signals, but it was up to e\ ach Host to supply its own connector.

That may have been the case at the very start, but when I was working with
IMPs at MIT (roughly '78 on), things were different. The 3 different kinds of
IMP interfaces (listed earlier; LH, DH, and VDH) were quite different,

To start with DH (by far and away the most common), IMPs had a specified round
'female' plug (a mil-spec connecter, available from AMP - like the one in the
URL Carsten provided - I think the axact part number is in the documemtation),
mounted on the back of the IMP somewhere. (MIT had a 516 IMP and a 316 TIP,
and later C30's, and I think the DH interfaces were all the same that way.)
Usually the host interface used something like a Berg (IDE) connector on the
PCB, into which plugged a short pigtail, on the other end of which was an
identical female plug, which mounted on the back of the host. A male-male
cable, using the same connector family, then connected the host to the IMP.

(I recall, early on at MIT, being the person who learned to make those
cables. There was a special tool which crimped the wires into the pins, and
other special tools to insert and remove the pins to/from the connector
shell. I have verified that host configuration for ACC LH-DH/11 and XQ/1822
host interfaces, and I'm pretty sure the ACC Multibus IMP interface was the
same. The QBUS IMP interface from SRI was, I think, similar; I found
documentation for it online at one point, but I don't have time to find my
copy to check it at this instant. I know it had the male-male cable, I made
one for it.)

I'm not sure about LH interfaces (MIT only had one, on MIT-MC); that may have
used a BBN supplied cable. Check the 1822 spec.

The VDH interface used a modem, and I have this impression/memory that the
IMP interface to that would have been the stock IMP/modem interface. What was
on the host end would have been whatever was stock for the modem interface
used. On the IMP end, I have a vague memory (from a day when we shut
everything down to reorganize the rat's nest of cables around the IMP+TIP)
that it was a hairy connector in which each pin was a coax job, with a ground
shell around a center confuction - but don't depend on that memory. The Bell
30x modem manual may give the details.


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