Been a long time, and I don't have the hardware in front of me. I figure the answer would be quicker here and more correct than looking it up

RCIS goes on the RCOU card right?
What it the RCOU has a daughter board (RCOS?)
Is there a card for that or is it all on the card that goes on the RCOU?

The RCIS is the daughter board for the RCIU. The RCOS is the daughter board for the RCOU. You cannot put an RCIS on an RCOU or put an RCOS on an RCIU. If you have a CIX release 4 or higher, you can use the BCOCIU which combines the two into one card.

no this is an old DK424

Thanks for clearing that up, I wasn't sure Where the RCIS lived. I had the RCIU and RCIS backwards in my head. thanks for setting me straight.
I guess my question (which you already addressed) was if I put the RCIS on the RCOS, would it control Caller ID for all 8 lines.
Since the RCIS goes on the RCIU, then it as a mute point.
Thanks again.
-Bill

All cards that are added as a daughter card to a main one have an 'S' at the end.

BDKS
RCOS
RCIS

Don't know what "S" stands for, may "Secondary?"

I believe the "S" stands for sub-assembly.