Core Plane Circuit Board

Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or rope core memory and also core plane.

Core uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bitof information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow for an individual core to be set to either a one or a zero and for its magnetization to be changed by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a zero, thus erasing it. This is called destructive readout. When not being read or written, the cores maintain the last value they had, even when power is turned off. This makes them nonvolatile.

     
 There was a development programme preceding the A-7 project called 'Integrated Light Attack Avionic System'  (ILAAS) and for this the Team Leader Jim Machin and the team  developed a 2K rope core memory Read Only Memory (ROM) from scratch as it was necessary to ensure non volatility and a very wide temperature range (in fact he achieved about -70C to around +120C).  The approach used large ferromagnetic cores threaded with a number of copper wires, threading or bypassing the ferrite cores. The design gave a store cycle time of around 1 microsecond. and avoided the ½ current drives of a conventional core stack. (For the subsequent A-7 HUD production a manufacturing source was established in Portugal drawing on their lace making skills.) The provision of reliable storage was a problem and a magnetic core store, of 2048 words, was used for the main program store. The new 16bit bipolar RAM was used for the data memory but to keep costs down this was limited to 64 words. In the A-7 the weapon aiming calculations were performed in a central computer and although such data as airspeed, height, aircraft velocity vector and altitude were provided to the HUD for generation of the symbology this design was not used  to carry out the weapon aiming itself. The original 18/12 processor used a programmable memory of 2K read only rope core memory. There was  a story that hese were assembled at one time  by the lace maker ladies of Portugal; following a workers revolution this was then shifted to the lace makers of Malta  and finally to Hong Kong. The production derivative extended the memory to 4k to allow for weapon aiming computation.