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CRAM, or Card Random Access Memory, was a mass storage device invented by NCR, which first appeared on their model 315 mainframe computer in 1962.

A CRAM cartridge contained 256 3x14" cards with a mylar magnetic recording surface. The cards were ingeniously suspended from eight d-section rods, which were selectively rotated to release a specific card, each card having a unique pattern of notches at one end. The selected card was dropped and wrapped around a rotating drum to be read or written. Each cartridge could store 5.5MB.

One "interesting" feature of this device was the potential for a "double drop", where two cards would drop at once, due to a break in a notch on one card. This would result in a high pitched noise with which operators were very familiar and would hear even outside the computer room.

Another interesting feature was that, should an operator accidentally drop all the cards from a cartdridge, they could be replaced without worrying about order. The order of the cards was not important because of the notch encoding system.

CRAM was very successful in the 1960's, offering a fast and secure storage alternative to magnetic tape, but was superceded by the development of superior disk drive technology.

CRAM is also an acronym for Challenge-Response Authentication Mechanism.