NCR CRAM
From Wikipedia, the free encyclopedia
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CRAM is an acronym for Challenge-Response Authentication Mechanism
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CRAM can mean chalcogenide random access memory (C-RAM)
[edit] CRAM, or Card Random Access Memory
model 353-1, was a mass storage device invented by NCR, which first appeared on their model NCR-315 mainframe computer in 1962.
| A CRAM cartridge contained 256 3x14" cards with a PET film magnetic recording surface. Each Deck of cards could contain up to 5.5 MB of alphanumeric characters. 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. Later versions of the CRAM; 353-2 and 353-3 used Decks of 512 card, thus doubling the storage capacity of each unit. The CRAM was also available on NCR's third generation NCR Century 100 as the NCR/653-100.
Each card contains seven tracks containing 1550 slabs each of them. Normally the track was initialized with a four slab header containing the cartridge number (2), the card number and the track number. |
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| Cards were dropped by changing the card rods to a binary configuration and release the two outside release rods. Air was blown over the top of the cards to keep them separated, and to increase the dropping speed. Once on the rotating Drum a series of positive and negative air pressure chambers pulled the card across a magnetic read-write head. After one or more passes over the head, where data is written to or read from the card, a release gate allow the card to be thrown along a raceway over the card deck, and onto a ‘’loader’’ mechanism. The loader used a group of electro-magnetic solenoids to slam the card back onto the control rods. The unit was a monster with two large electric motors that drove four large vacuum/blowers. It was possible to have up to five cards in motion at any point in time; one dropping, one on the drum, two in the return transport, and one being load back onto the deck.
If the card didn't succeed in dropping there was a "magic wand" similar to a pencil available to solve the problem. 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 cartridge, 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 superseded by the development of superior disk drive technology. |
