Core memory in IBM mainframes from 55 years ago

Did you know that computer memory used to be stored in cores linked by hand-woven nets of copper wire?

The core was a small ferrite ring (iron because magnetic), and wires were woven between them to read or set the electrical current in that magnetic ring (which ran clockwise or anti-clockwise depending on the value). This direction represented “on” or “off” (1 or 0). Each ring stored a single bit, and there are eight bits in a byte, so 128 kilobytes required over a million ferrite rings.

You can read more in A look at IBM S/360 core memory.

A 64 KB core array from the IBM S/360 Model 50. There are 18 core planes stacked front-to-back. The blue cables are the sense/inhibit lines. Driver cards are plugged into the front of this array.

I recently received a vintage core memory array, part of an IBM System/360 mainframe computer. These arrays were used in a 128-kilobyte core memory system that filled a large cabinet weighing 610 pounds. This article explains how core memory worked, how this core array was used in mainframes, and why core memory was so bulky.

[…] depending on the particular computer, 128K weighed 575, 610, or 750 pounds.