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Comment by gchadwick | Hacker News Reader

I do wonder why they decided to have have separate shell size and pin designations given there appears to be a 1:1 correlation between shell sizes and pins (i.e. the 'B' shell is always 25 pins, the 'E' shell is always 9 pins). Perhaps there was plan to have fewer pins in the same shell at some point?

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it's not always 9 pins. you can get pretty creative regarding the number and type of pins (high current, coax) you can fit in that shell:

DE with 2 High current contacts:

https://de.wikipedia.org/wiki/D-Sub#/media/Datei:D-Sub_conne...

DE with 15 contacts ("VGA"):

https://de.wikipedia.org/wiki/D-Sub#/media/Datei:D-SUB_DE-9-...

https://en.wikipedia.org/wiki/File:D-Sub_connectors_size_DE_...

https://en.wikipedia.org/wiki/File:D-SUB_DE-9-F_BLUE_VGA_IMG...

There's also 13-W3: DB shell, 13 pins, 3 of them coax: https://en.wikipedia.org/wiki/DB13W3. They were used for high-end workstation video back in the day.

I came here to share this cursed connector. I remember it well from Sun workstations

VGA connectors used the same shell as the DE-9 but had three rows for a total of 15 pins.

An excellent example I really should have been able to think of myself!

And for reasons I don't fully understand, somewhat unrelated - if you look around almost any small business in my area, it's almost always VGA, rarely DVI, almost never HDMI or DisplayPort.

My theory is just that the cables came in the box and are screw-on when more modern connectors are friction fit, and the IT departments don't want the hassle of "they just got pulled out." Which should have been predictable - but I can literally see 12th gen Intel, paired with 1080p display, over VGA fairly regularly.

DisplayPort has latching connectors, but they're easily broken when pulled out without unlatching.

For some reason DisplayPort monitors are more rare, and even when you get one like the MSI Pro MP241, it comes with an HDMI cable in the box!

It's 100% because the VGA cable came in the box. Nothing about cables pulling because my lazy counterparts would not even screw in the DE15 cables half the time.

Source: Too many years experience in the desktop support trenches.

Confusingly enough, I’ve actually seen real, properly named DB-9 connectors. They were a cheaper version of a DB-25 to DE-9 converter. Instead of combining the extra pins properly, they just had a DE-9 on one end connected to only 9 pins on the DB end. They sometimes occasionally even worked properly at low enough line rates.

DE15 and DA15 both exist and are pretty commonly used, I'm not aware of any other conflicts in normal versions.

However, you can get weird Dsub connectors with things like COAX in there, so having the shell sizes have names can be useful.

Coax and high-current/voltage pins are not that weird. You can also get truly weird semi-proprietary pins like fiber optics or even pneumatics/fluidics.

IMO, the issue is less that there is a shell designation and more that the shell designation is hard to interpret.

A single letter doesn't have a lot of meaning on its own, and the A-E order is not consistent with the E shell being smaller than all the others.

By making it fully adjacent to the 'D', it makes the letter sound like it's part of the standard's name, like the 'RJ' in 'RJ45'.

It would have been better to focus on pin count and row count, as those along with standard pin spacing drive the shell size.

D-2R-15 for a two row 15 pin connector equivalent to DA-15, D-3R-15 for a 3 row 15 pin equivalent to DE-15 / VGA.

Could trim out the 'R' and go with "D2-15" for 2 row and "D3-15" for 3 row, if brevity is preferred.

I use both DA-15 and DE-15 all the time in my line of work, and I am fastidious about using the correct terminology on all my drawings. Manufacturers are ironically some of the worst at getting this right.

I vaguely remember there being some proprietary connectors that were the same as the standard with a single pin missing.

IBM did that pretty often. And well, the original VGA connector had pin 9 missing and used as a key.

You might be thinking of VGA connectors, which were a DE-15 connector, similar to a DE-9 serial cable, but with an extra row of pins and often pin 9 missing.

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