1. In a Redundant Array of Independent Discs (RAID) memory disc array, an apparatus for generating dual parities P and Q, the apparatus comprising: a dual XOR engine for performing a plain XOR operation for parity P and for performing a weighted XOR operation for parity Q; wherein said plain and weighted XOR operations are performed in a single pass; and a memory controller having a memory addressing arrangement including a dual XOR field parameter and an offset field parameter for encoding instructions for generating said dual parities.