The control area was called the Main Control Unit (MCU) and there were two provided on the model for security although a maximum of 12 could have been provided. Each MCU was capable of handling approximately 6,000 instructions per hour. The MCU operated in accordance with an instruction program stored in the form of a number of wires threading a bank of magnetic cores. Changes in the operating sequence can be obtained by program changes involving the re-threading of a number of wires in the store instead of by widespread re-wiring within and between a multitude of separate units.