Description attached to folder: "Set of original blueprint schematics (20) for Magnetic Drum storage fitted as an additional temporary storage in 1960 to LEO II/III. (The alternative temporary storage was the Mercury Delay Line fitted from new in 1958 but this was highly temperature sensitive. The monitor unit from this is part of this collection). Example payroll: The LEO system used Hollerich cards for permanent storage. A card for each employee would be fed into the card reader, current data, hours worked, overtime, bonuses etc. would be fed in off paper tape. After calculation the results would be stored on the magnet drum and the output from this would then be used to produce a new set of Hollerich cards with the accumulated tax paid and other details for use on the next payroll run."