@misty one of those pins is a "ring indicator" for modems for instance, that one is not present on the db9 connector.

It's also possible to have a whole extra channel on the 25pin, like a whole extra pair or Rx/tx lines with all of the other signals. I don't know if any PC ever actually implemented those though.

@misty oh, one more thing, there *are* db9 to db25 converters that also helpfully turn the cable into a null modem.

These are rare but they do exist and if you get one you might spend a lot of time and effort on buying new USB serial cables for no good reason.

I will not be answering any questions about how I know this. 😐

@misty I think I still have it. It has a fancy label printed sticker on it that says ☠️CURSED☠️ now. 😄