BC11A UNIBUS cable
The BC11A UNIBUS cable is used to connect together UNIBUS elements (such as CPUs, system units, and free-standing devices such as the RP11 disk controller). It carries all 56 UNIBUS signals, and 64 ground lines (alternating with the signals, to prevent crosstalk).
It consists of a pair of 60-conductor flat cables ('Flexprint' - they contain flat traces, not wires) separated by a foam layer (probably to precent crosstalk, or maintain a constant impedance). On each end is a short dual PCB (M919 and M929), which plugs into the 'UNIBUS in' or 'UNIBUS out' slot of the element's backplane.
It comes in standard pre-manufactured lengths, from 2 feet up to 50 feet.