The IBM 3612, 3624 and 3600 communications protocols were incompatible with other ATM vendor's high-level communications protocols. The 3624 was eventually replaced by the IBM 473x series of ATMs which were unsuccessful. Part of the reason for the failure of the IBM 473x to take hold in the ATM marketplace was the lack of a backward compatibility to the 3624 protocol when it was introduced. One of the most lasting features introduced with the 3624 was the IBM 3624 PIN block format used in transmission of an encrypted personal identification number (PIN). The PIN functions, with an early commercial encryption using the DES algorithm, were implemented in two modules - BQKPERS and BQKCIPH - and their export controlled under the US export munitions rules. References External links A brief mention of the 3624 protocol from IBM Automated teller machines Diebold 3624