chad | = C = | chain

chad box n.

A metal box about the size of a lunchbox (or in some models a large wastebasket), for collecting the chad (sense 2) that accumulated in Iron Age card punches. You had to open the covers of the card punch periodically and empty the chad box. The bit bucket was notionally the equivalent device in the CPU enclosure, which was typically across the room in another great gray-and-blue box.

chad | = C = | chain