Unibus equipment, left to right :-
Single card device controllers had bus grant signals daisy chained through each slot. If a card was removed or a slot left empty, a continuity card had to be inserted in the correct slot in the backplane. In addition, the grant for NPR (non-processor requests [DMA]), where jumpered on the backplane and a wire wrap lead had to be inserted or removed.
The card on the right is the original knuckle busting card where you lost skin off you hands every time you installed or removed one. The newer card on the left was full length and easy to install, and in addition, it correctly daisy chained the NPR grant line saving the task of changing backplane wire wraps.