A High-density file drum as a computer store

The paper describes a large-capacity magnetic drum store having a capacity of ¿ 15,000,000 bits and an average random access time of ¿ 200 millisec. A packing density of just over 1,000 bits per in. has been obtained by floating specially designed heads on a film of oil which automatically maintains a spacing of 0.002 in. between the head and the drum surface. Special considerations led to the use of a copper-nickel-iron alloy for the drum surface. A self-clocked reading system is used to obviate the need for high mechanical stability. The reading circuit also has special features which keep it operating under optimum conditions over a range of signal amplitudes.