D subminiture connectors Re: Anyone recognize this PCB?

der Mouse mouse at Rodents.Montreal.QC.CA
Fri Aug 18 15:19:24 CDT 2006

>> BTW the B in DB refers to the size shell.  The 25 pin connectors
>> used on the original IBM are B size.  Other sizes use a different
>> letter ie DE, etc.  But a lot of people call every size "DB"

Until relatively recently I was one of them. :-(

> So what letters are used for other sizes?

DA is the 15-pin size, the one used by AUI Ethernet back in the heyday
of 10base5.

DB is the 25-pin size, the one that's standard for serial ports
(de-jure standard, not the 9-pin de-facto standard).  Also used for
peecee parallel ports and older Macintosh SCSI, and doubtless a bunch
of other things too.

DC is a size I almost never see, and I don't remember the exact pin
count.  37?  39?  Something like that.

DD is a much larger size, supporting 50 pins.  Some of the older Sun
equipment uses this for SCSI, which is the only use I know it from.

DE is the small size, used with 9 pins for the serial connectors I
mentioned above and with 15 pins for peecee video ("VGA").

I don't know why the order makes so much sense for DA through DD and
then goes wonky for DE.  I conjecture that when it was originally
planned, nobody expected it to be used for anything that small, so the
DE was tacked on as an afterthought.  (I suppose they could have used
D@, but that would make sense only to geeks who know their ASCII. :)

I also don't know whether there are any other sizes with names.  Other
sizes, though rare, do exist; for example, NeXT used a D-shell
connector of an odd size, with something like 19 pins, to drive their
greyscale video displays.

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