@misty on the 25pin side of things: almost certainly not. Most of those 25 pins never really got used. Caveat for speciality devices, but anything you likely have laying around: almost certainly won't matter.
As for being compatible, there's only a handful of USB to rs232 chipsets around. At least on Linux I've never ran into one that didn't just work. I'm assuming that windows also just comes with those drivers at this point.
No idea about macOS, but I similarly can't imagine problems.
@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. 😄
