Magnetic-Core Memory
The dominant form of computer memory from the mid-1950s to the mid-1970s, made from tiny magnetized rings threaded onto wires.
Core memory stores each bit in a small ring of ferrite. Wires run through the ring, and a current in the right pattern sets the ring's magnetization one way or the other. Reading a bit resets it, so the controller writes it back afterward.
The technique was developed in the early 1950s by several groups. Jay Forrester's team at MIT installed a core memory in the Whirlwind computer in 1953. Early cores were strung by hand, often by workers in Asia, and the price per bit fell steadily until semiconductor memory replaced the technology in the 1970s.
Why it matters
Core memory was fast, reliable and kept its contents when the power went off. It made large, dependable computers possible, and the word 'core' stayed in programmer slang, as in 'core dump', long after the rings were gone.
Key facts
- Each ring stored one bit.
- Developed at MIT and used in Whirlwind in 1953.
- Rings were threaded by hand.
- Retained data without power.
Sources
- Campbell-Kelly, Martin, and William Aspray, et al. Computer: A History of the Information Machine. 3rd ed. Westview Press, 2013.
- Pugh, Emerson W. Memories That Shaped an Industry: Decisions Leading to IBM System/360. MIT Press, 1984.
- Computer History Museum online collection catalog (computerhistory.org/collections).