I've always wondered about this as well. There are several of these cards at my local surplus place. I examined the traces, once in the past, but I wasn't able to determine exactly what they were for.

If I had to take a wild guess, it might have something to do with some proprietary modem/telephony feature on Compaq motherboards. But that's just a guess.

Yeah that's my assumption, some sort of audio integration with the modem for speakerphone.

If I'm not mistake, these extra pins were for Compaq computers.

They were used to route audio to a front panel, the CD drive or something like that, I think.

Edit: Or for the modem, as you already said. 😀

I remember having extracted one such ISA card with that 3rd little batch of pins and iirc it was indeed a Compaq.
Never got around to test it though, but I did do some reading years ago as I was curious and just wanted to add that I "thought" at the time it might have something to do with the internal speaker or something. Could also be for something else, but I wasn't really interested anyway (because proprietary) so never bothered to dive further into the matter.

Jo22 wrote:

If I'm not mistake, these extra pins were for Compaq computers.

They were used to route audio to a front panel, the CD drive or something like that, I think.

Edit: Or for the modem, as you already said. 😀

I think you're correct about routing audio. I tried to follow the traces as best I could, and it looked like it met with the CD-Audio channels. There are several of these at my local place for $3 or so--I'm tempted to just get one and clip the rear pins off to see if it still functions normally.