Those D connectors


Ken Pogran (pogran@ccq.bbn.com)
Fri, 17 Jun 88 08:14:52 EDT


(Say, don't we have a "components" mailing list or something?
This hardly seems like something for TCP-IP. Oh, well.)

I thought a bit of history might be interesting: The "D-series"
connectors made their debut in the 1950s to interconnect military
electronics "modules", which at the time were assemblies in metal
boxes that plugged into "pans" and "trays". Interestingly, they
were NOT designed for cable applications and they were NOT
designed to support weight: the modules in their little boxes
were supported mechanically by the pans and trays. The
connectors were, however, pretty rugged -- they were all MIL-SPEC
varieties. By the way, to give an idea of the size and scale of
things at the time, they were referred to in 1960s connector
literature as "D-subminiature" connectors.

The Bell System began the large-scale use of these connectors on
cables with the introduction of DataPhones (Bell's trademark for
their modem service). Remember the rather ornate-looking light
gray hard plastic shells?

One advantage of the D-series connectors was the density of pins,
and their use really took off -- especially for cable
applications, precisely what they were NOT designed for!
Manufacturers have tried a lot of ideas to cope with cables and
their weight, with not a lot of success; the basic design of the
connectors just isn't intended for it. And couple that with
cost-reduction efforts (seen any MIL-SPEC versions of these
connectors in products you've bought recently?) which have made
many of the connectors even flimsier and you have a recipe for
trouble.

On the other hand, there's the overkill approach: The old,
nearly-impossible-to-get $75 48-series round connector that BBN
spec'ed a long, long time ago for the 1822 Distant Interface
connector ... (since replaced by a 37-pin D connector, of
course!)

Ken Pogran



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