The technique of using magnetic thin films in computer memory devices is reviewed, and conclusions drawn as to the properties of the film that are required for successful operation of a memory. A description is then given of a series of experiments which were designed to determine the best compromise in properties. Particular importance is attached to the easy axis dispersion, and it is claimed that the addition of a small quantity of cobalt to the nickel iron alloy reduces this despersion by about a factor 3.