Jay W. Forrester and the Invention of Magnetic Core Memory

February 09, 2024 by Robert Keim

During his long and remarkably productive career, Jay Forrester accumulated an impressive list of innovations and achievements in electrical engineering, social science, and business management.

The uniquely rapid cultural, technological, and political changes of the twentieth century allowed certain individuals to lead lives of extraordinary diversity and adaptability. Jay W. Forrester was one of those individuals—and for someone like me who grew up in a thoroughly modernized and computerized era, there is something especially marvelous about a man who began his life on a non-electrified cattle ranch, studied engineering at MIT, saw combat as a technical advisor aboard a World War Two aircraft carrier, developed one of the first digital computers, founded a field of study known as system dynamics, and eventually returned to MIT as a professor of management.


Jay Wright Forrester (1918–2016)

Jay Wright Forrester (1918–2016). Image courtesy of the National Academy of Engineering

Lessons From the Farm

Born in 1918 and raised on a remote homestead in central Nebraska, Jay Forrester’s childhood environment didn’t exactly surround him with the latest technology. However, agricultural life gave him many opportunities to develop traits and abilities that would prove crucial to his career as an engineer and scientist.

If you’ve lived in or near Nebraska, you know that a year-round, outdoor job in that sort of climate is likely to produce a young man of great perseverance and interior strength, but beyond that, the various difficulties and small crises that continually arise on a working homestead demand ingenuity and resourcefulness. I suspect that Forrester’s problem-solving skills were well honed long before he started working as an engineer, and in fact, one of his first engineering projects was a windmill—built from parts scavenged from old vehicles—that functioned as the farm’s first source of electrical power.


Feedback and the Founding of System Dynamics

Forrester left his hometown to study electrical engineering at the University of Nebraska in Lincoln, and then he went to MIT for graduate studies, eventually completing a Master’s degree. He started as an assistant in the High Voltage Laboratory and later transferred to a new research department that developed servo-based controllers for military equipment. That’s how Forrester ended up spending time on a naval vessel—in 1943 the aircraft carrier Lexington was fitted with a prototype servo system for controlling its radar assembly, and when the ship was deployed, he volunteered to stay aboard and provide technical support.


The USS Lexington in 1943

The USS Lexington in 1943. Image courtesy of M. Hansen via Wikimedia Commons [Public domain]

A servomotor is defined as a mechanical actuator that incorporates position feedback, and Forrester’s work in MIT’s Servomechanism Lab ensured that he had ample time and motivation to ponder the nature and effects of feedback in engineered systems. In a particularly thought-provoking example of knowledge transfer between the physical sciences and the social sciences, Forrester later realized that he could use feedback theory to analyze and improve complex processes involved in the management of large businesses.

His initial research pertained specifically to General Electric Corporation and the company’s inability to eliminate inventory and employment oscillations, but this project evolved into system dynamics, a generalized field of study that emerged from Jay Forrester’s work in the 1950s and his 1961 book Industrial Dynamics. The basic premise of system dynamics is that simulation, feedback, and mental models can help us to understand and improve complex human systems.


Magnetic Memory

Jay Forrester has received much recognition and acclaim for his pioneering work in social dynamics, but I have to admit that as an electrical engineer, I’m more interested in his contribution to early computer systems.

Memory may seem like a rather mundane portion of a computer when compared with the impressive complexity and sophistication of a central processing unit. Nonetheless, memory was a serious limiting factor in the early days of digital computing, and Forrester’s invention—ferromagnetic memory—was a crucial step forward in the industry’s journey toward compact, high-performance computer hardware.

Before ferromagnetic memory, computers used storage technologies that nowadays seem primitive with regard to their performance but rather exotic with regard to their mode of operation. Acoustic delay lines stored data as sound waves, and electron-beam devices used cathode-ray tubes to store data as electric charge. In addition to their limited density and elaborate construction, these types of memory required periodic refreshing (as does modern DRAM).

Ferromagnetic memory was a major improvement. Compared to its predecessors, it was easy to manufacture, inexpensive, and reliable. It also allowed for higher storage density, and it was nonvolatile: once the bit was stored, it didn’t need to be refreshed. The diagram below conveys the structure of magnetic memory:

Diagram of the structure of magnetic memory

The drive circuitry allows each magnet to function like a digital latch: current generates magnetic fields that set or reset a magnetic “bit,” and this magnetic state remains after power is removed. You can read more about the operational details of magnetic memory in the AAC textbook.

Various researchers contributed to the development of magnetic memory modules, but Jay Forrester brought it all together into a functional, practical system. He obtained a patent for the invention of random-access coincident-current magnetic core memory in 1956, an accomplishment for which he was eventually inducted into the National Inventors Hall of Fame—but that occurred after he had spent years in patent courts defending his claim to be the principal inventor of this foundational technology for the burgeoning computing industry.

Forrester’s invention was the dominant form of memory until semiconductor devices prevailed. He called it “the solution to a missing link in computer technology.”


From Electronic Systems to Social Systems

Perhaps acting in accordance with a homesteading, frontier spirit that he inherited from his father, Forrester decided—in 1956!—that the era of computer pioneers was over. He turned his attention to business management, and I commend him for so insightfully and creatively applying his technical expertise to the social and business sciences.

Jay W. Forrester died on November 16, 2016, at the age of 98. His biography is adorned by a long list of awards, recognitions, and honorary degrees, and he was known for his quiet, courteous manner and edifying conversation. I never met him, but he certainly seems to have been an exemplary engineer, a dedicated intellectual, and a gentleman.



Featured image courtesy of MIT.