patchboard vs plugboard

patchboard

noun
  • A component of a manual telephone switchboard, or of various early data processing equipment, in which circuits are completed with cords on a matrix of connections. 

plugboard

noun
  • An array of jacks or hubs into which patch cords can be inserted in order to complete electrical circuits. 

How often have the words patchboard and plugboard occurred in a corpus of books? (source: Google Ngram Viewer )