This is definitely off topic from photography....

On the back of my PC, there are two knock-outs, near the bottom of the case. These knock-outs are 1/2" x 3" long. It's not the typical PCI slot cover, nor does a low profile slot cover work in these openings. Just a couple of holes on either side of the long ends, for attaching some sort of card, with small bolts/nuts, I presume.

The mother board does not have any PCI sockets near these knock-outs.

I presume that this space could be used for attaching some sort of circuit board to, but what?

Any help on what these empty spaces are potentially used for, I would appreciate it.