The memory of the IBM 1620 is organized into 6-bit addressable digits, the usual "8, 4, 2, 1" plus "F", used as a flag bit and "C", an odd parity check bit. BCD "alphamerics" are encoded using digit pairs, with the "zone" in the even-addressed digit and the "digit" in the odd-addressed digit, the "zone" being related to the "12", "11", and "0" "zone punches" as in the 1400 series. Input/Output translation hardware converted between the internal digit pairs and the external standard 6-bit BCD codes.