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---
title: Magnetic_core_memory
tags: [computer-history, memory]
created: Friday, September 27, 2024
---
# Magnetic_core_memory
![](../img/magnetic-core-memory.jpg)
Like [Magnetic_drum_memory](Magnetic_drum_memory.md), magnetic core memory was
faster and more reliable than [delay_line_memory](Delay_line_memory.md) and
vacuum-tubes, and was also persistent.
It worked as follows. Magnetic beads made of ferrite and threaded with copper
were arranged in a crisscross grid. A bead would be placed at the overlap of two
copper threads. This constitutes a "core".A pulse of electric current would
magnetise/de-magnetise the cores.
![](../img/magnetic-core-closeup.jpg)

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zk/The_History_of_Computing_Swade.md
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@ -542,7 +542,7 @@ manage payroll in business contexts.
Focused primarily on business applications and targetted at businesses rather Focused primarily on business applications and targetted at businesses rather
than government contracts. Less powerful than the 701. than government contracts. Less powerful than the 701.
### IBM 650 ### IBM 650 (1953)
![IBM 650](../img/ibm-650.jpg) ![IBM 650](../img/ibm-650.jpg)
@ -562,4 +562,48 @@ that would go on to work at IBM.
Donald Knuth dedicated _The Art of Computer Programming_ to the 650. Donald Knuth dedicated _The Art of Computer Programming_ to the 650.
It used magnetic drum memory along with vacuum-tubes. It used [magnetic drum memory](./Magnetic_drum_memory.md) along with
vacuum-tubes.
### IBM 1401 (1959)
## Magnetic core devices: Whirlwind and SAGE
Two devices that leveraged the new technology of
[magnetic_core_memory](Magnetic_core_memory.md) where the Whirlwind and SAGE
computers. The ENIAC was also updated to use magnetic cores.
![Whirlwind magnetic core memory](../img/whirlwind-magnetic-cores.JPG)
The Whirlwind computer (1953) was a flight simulator and the first to use
magnetic cores. Crucially was able to operate in realtime for output.
The SAGE computer (_Semi-Automatic Ground Environment_) emerged as a response to
the Soviet acquisition of the atomic bomb in 1949. The Americans realised they
needed a much better early warning and air defence system that would allow them
to identify bombers in their airspace and dispatch fighters.
To achieve this, it was necessary to detect enemy bombers with radar and compute
an interception course. Alterations in the bomber flight path required
continuous updates and real-time computation of directions for the responding
fighter.
The resulting computer was SAGE (made by IBM) which was modelled on Whirlwind,
using magnetic cores. SAGE computers were spread accross the continental US in
sectors and managed by NORAD.
![SAGE command post](../img/SAGE_command_post.jpg)
The SAGE system was operation between 1958-1984, receiving continual
improvements and updates. In addition to magnetic cores it introduced many
technological innovations that influenced computers generally: interactive
screens, printed circuit boards, mass-storage devices, digital communication
over telephone lines, time-sharing, along with advances in software.
Because so many private companies worked as contractors on SAGE (IBM, Burroughs,
Bell Labs, RAND Corp), the military technology (both hardware and software) made
its way from the military context to business and consumer computing.
An example of a civilian application of SAGE technology was airline booking
systems, where booking reservation data needed to be processed in realtime. IBM
worked with American Airlines to introduce this.