Some IOA cards, in some situations, require a second card, an IOP.
IOA = Input/Output Adapter
IOP = Input/Output Processor.
The IOA will have the physical ports to hook up cables and is usually to
the right of the IOP, which has no ports.
Here's an example:
2844 is the IOP
5704 was a scsi IOA
3576 was a SCSI tape drive.
Cable went from the 5704 to the external tape drive.
Some of the same cards may have needed an IOP only if used by IBM i, but
if used by Linux, could not use an IOP.
I skipped the power 7 but on the Power 8 you can not use any IOP's.