D-shell sizes [was Re: Slightly rare Mac 512k with D(?)-25 connector]

der Mouse mouse at Rodents.Montreal.QC.CA
Wed Sep 5 10:47:30 CDT 2007

> [...] a 25-pin D connector reminscent of the Mac "SCSI" connectors on
> Mac Plus and other machines.  [...]

> Forgotten what the correct designation for those D-connectors is, and
> wanted to get this out fast in case anyone wants it.

The 25-pin size - the one used for the MAC SCSI you refer to, the one
called for by the mechanical portion of the RS-232 spec, the one used
for peecee parallel ports - is DB.

Using pin count for that same pin spacing, the table is DA=15, DB=25,
DC=39 (I think), DD=50 (three rows), DE=9.  The DE shell is also used
in a 15-pin variant ("VGA"), but the pins are spaced substantially
closer than in the DE-9.  DA is probably best known for peecee joystick
connectors, but it also got used for AUI Ethernet back in the 10base5
days, before even 10base2, much less 10baseT.  DC doesn't get used much
in my experience; I think I have a few SBus cards that use it for the
fat end of their octopus cables.  DD was used by Sun for SCSI back in
the Sun-2 and Sun-3 era, and also got used for IPI disks.  DE is
probably best known for peecee serial ports and "VGA" video (a lot of
people don't realize the shell size is the same for those two), but
I've seen it used for other things, such as Sun-3 monochrome video.
I'm sure each size has plenty of other uses I know nothing about, too.

I don't know why they are out of order.  I speculate that someone
designed DA through DD, never expecting D-shell to get used for
anything under 15 pins, then had to tack on the 9-pin size later.
(Arguably they should have called it D@, but that would probably have
been too geeky. :)

There exist D-shell connectors of other sizes, like the NeXT "black"
hardware video connector (which held something like 19 pins).  I don't
know whether they have names in the DA..DE series; I suspect they have
no standard names because they're not standard sizes.

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