Core Memory
The first magnetic core memory, from the IBM 405
Alphabetical Accounting Machine. The photo shows the single drive lines
through the cores in the long direction and fifty turns in the short
direction. The cores are 150 mil inside diameter, 240 mil outside, 45 mil
high. This experimental system was tested successfully in April 1952.
Of course IBM 360 core memory was much more advanced and denser.
The photo shows a magnetic core plane of the type used in the 360.
The IBM 2361 Core Storage Module housed 1MB or 2MB bytes of core memory,
depending on the model. You can
see the core planes (and the individual cores, i.e. bits) through the glass
doors.
Core memory diagram, illustrating coincident current selection. The
half-select current applied through the indicated vertical and horizontal
lines are each too small to switch the cores through which they pass. The one
core in the center of the figure is switched, however, by the coincidence of
the two currents. A former IBM employee tells me that when IBM first decided
to manufacture core memory, they consulted with the Lifesaver company on
fabrication methods.
Allen J. Palmer adds (March 2005): "I am part of the
Computer History Museum
1401
Restoration Project team (729's being my area for this project). I was
looking at your web page on core memory. Do you have a page with the full
diagram of the core wiring layout. There were 4 wired passing through each
'donut' -- X & Y plus the read wire which sensed the flip of the core at
read out by the magnetic field developed when the core flipped & that field
'cut' the read wire & inducted an 'electrical impulse' which was then
amplified and became the 'read out data'. A 4th wire was the 'inhibit' wire
used prevent some core from flipping' I have an old 4k 1401 memory core
sitting out on my work bench gathering dust for the last 25 years. Someday I
need to clean it up & build a case with a light & a magnifying glass so
people can see how we did it in the 'old days'."
Source: [4].
Links:
- The IBM 737 Magnetic core storage unit (1954, for the IBM 701)
- IBM 2361 core storage unit, IBM Archives website (accessed 7 February 2019).
- IBM 2361 Large Capacity Storage, Wikipedia (accessed 7 February 2019).
- Core Memory: A Visual Survey of Vintage Computers
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