The 3624 was marketed in eight different versions. The 3624 Version 8 incorporated use of a six-row by forty-column dot-matrix customerdisplay, four line by 34 character statement / journal printer, labeled function / account keys, one to two currency cartridges and an optional depository. Earlier models, such as the Version 2, featured a smaller two-line display. Unusual by today's standards, the customer's ATM card was inserted with the magnetic stripe up. Modern ATMs typically are built to expect customers to insert their card with the magnetic strip facing down, although this can be changed to the opposite orientation. The transaction records printed by the 3624 and used by customers to verify their transactions were approximately 3 inches square and on similar card stock to punch cards. When performing deposits, customers were instructed to place a special transaction record inside of the deposit envelope to aid in the processing of the transaction by the back officestaff. An unfortunate design characteristic of the 3624 was that the vault that contained the cash dispenser was located in the upper area of the unit, making it top-heavy. This made the 3624 an extremely awkward machine to transport up and down stairs. Another complaint against the 3624 was the relatively small size of the cash cartridges in comparison to other vendors' equipment at the time. As was typical for ATM hardware of this era, the IBM 3624 had a two distinct high-level communications protocols. The first, a direct mainframe attachment through SDLC links was an IBM SNA LU0 protocol. The second was an attachment to the IBM 3600 and 4700 series of banking equipment, and was a start stop TDM loop with time slots assigned to specific 36xx series equipment at 1200 bit/sec. 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. 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.
