Magnetic-core memory

Magnetic-core memory stores bits by magnetizing tiny ferrite rings threaded with wires. It was a durable, nonvolatile form of random-access memory used in computers before semiconductor memory became dominant.

Magnetic hysteresis: The dependence of a material’s magnetization on its magnetic history, including its response to changing magnetic fields. Ferrite cores retained one of two magnetic states after the selecting current disappeared.
Ferrite: A ceramic material composed of iron oxide and other metal oxides, often used for its magnetic properties. Ferrite rings provided the stable magnetic states that represented stored bits.
An Wang: A Chinese American computer scientist and entrepreneur who developed early magnetic memory devices and founded Wang Laboratories. Wang’s 1949 patent described a pulse-transfer device that helped inspire core-memory development.
IBM 704: An IBM scientific computer introduced in 1954, notable for hardware floating-point arithmetic and magnetic-core memory. Its core memory supported demanding scientific calculations and became a defining feature of the system.
Semiconductor memory: Computer memory that stores data using electronic properties of semiconductor devices. Semiconductor memories eventually offered greater density and lower cost than magnetic-core arrays.
Coincident-current memory: A magnetic memory scheme that selects a core by applying partial switching currents through its row and column wires. This addressing method selected one core without switching the other cores on its row or column.
Magnetic core: A small magnetizable component that stores information through its magnetic state. Each ferrite ring in the array was one magnetic core and held one bit.
Jay Forrester: An American computer engineer who developed magnetic-core memory for the Whirlwind computer and later pioneered system dynamics. Forrester led the engineering work that made core memory practical for Whirlwind.
Apollo Guidance Computer: The onboard computer that guided Apollo spacecraft using real-time computation and compact integrated circuits. Its erasable memory used magnetic cores, while woven core rope stored fixed programs.
Dynamic random-access memory: Volatile semiconductor memory that stores each bit as charge in a capacitor and must be periodically refreshed. DRAM replaced core memory in many systems as chip capacity and manufacturing economics improved.

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