core storage

A non-volatile memory that holds magnetic charges in ferrite cores about 1/16th" diameter. The direction of the flux determines the 0 or 1. Developed in the late 1940s by Jay W. Forrester and Dr. An Wang, it was used extensively in the 1950s and 1960s. Since it holds its content without power, it is still used in specialized applications in the military and in space vehicles.

The cores (bits) are written by sending pulses with half the maximum current down each of the X and Y wires that will intersect at that core location. The direction of the pulses determines the magnetization (0 or 1). The core that receives both pulses is the one effected because it receives more than half the current. Reading is accomplished by a "destructive" read. A "0" is written to the core, and if the core was originally a 0, the sense wire receives no current. If it was originally a 1, current is sensed. The final step to complete the read is to rewrite the bit.

In 1956, IBM paid Dr. Wang $500,000 for his patent on core memories, which he used to expand his company, Wang Laboratories. See MRAM and early memories.

Core Storage

Core storage is why the internal workspace of the computer is called "memory." Like magnetic disks, magnetic cores hold their content without power.

Cores from the Whirlwind

In 1952, this core plane from the Whirlwind I computer held 256 bits of memory. Today's memory chips occupying the same amount of space hold billions of bits. (Image courtesy of The MITRE Corporation Archives.)

Just 12 Bits

This blowup of the Whirlwind core plane shows the detail of the wiring between the cores. (Image courtesy of The MITRE Corporation Archives.)