Diode matrix

A diode matrix is a two-dimensional grid of wires: each "intersection" wherein one row crosses over another has either a diode connecting them, or the wires are isolated from each other.

It is one of the most popular techniques for implementing a read-only memory. A diode matrix is used as the control store or microprogram in many early computers. A logically equivalent transistor matrix is still used as the control store or microprogram or 'decode ROM' in many modern microprocessors.