Read-Only Memory (ROM)
A Read-Only Memory (ROM) is a combinational circuit with n address-line data inputs (A0, A1, ... An-1) and b ( D0, D1, ... Db-1 ) data outputs. A ROM literally store the truth-table (minterms) of an n-input, b-output combinational circuit.
m A ROM is nonvolatile memory. That is, its contents are preserved even if no power is applied.