Plug-board
A plug-board was a mechanism which allowed users to easily configure early electro-mechanical digital computing devices (typically punched card equipment) to perform a given desired information-handling task; and, moreover, quickly and easily switch from one configuration to another. It generally consisted of a rectangular slab of non-conducting material such as Bakelite, with a regular array of holes; the holes contained pins or sockets, with jumper wires connecting them.
The jumpers allowed the connection of the various computational elements within the device (counters, adders, etc), as well as the input and output devices, in whatever way was needed to accomplish the desired information-handling goal. The complete assembly could be removed as a unit, and rapidly and easily replaced with a different one; the computational elements within the device were all connected to fixed locations on the plug-board, which allowed one plug-board (configured for one particular information-handling task) to be swapped for another. (Plug-boards were not intended principally for experimentation, but for configuration and fast conversion.)
