A CRAM cartridge contained 256 3x14 inch cards with a PET film magnetic recording surface.
Once on the rotating "drum" a series of positive and negative air pressure chambers pulled the card across a magnetic read-write head.
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 loaded back onto the deck.
This would result in a high pitched noise with which operators were very familiar and could hear even outside the computer room, and damage to the cards.
CRAM was very successful in the 1960s, offering a fast and secure storage alternative to magnetic tape, but was superseded by the development of superior disk drive technology.