Vermont Research Corporation used a gear shaper to cut extremely fine teeth into the edge of an aluminum disc. (We have probably the only cutter still in existence.) The “gear” teeth were filled with a magnetic substance and the tops of the teeth ground down so that the magnetic material had a little separation between the units. A magnetic reader would take note of what was passing by.
This drum – inside the housing – is 18 inches in diameter, 117 Volts, 60HZ, 3527 RPM, and 32 tracks.
Canada’s museum of science and innovation, the Ingenium, has a later model that apparently stores 500 KB. For reference, this desktop computer stores 237 GB, which is 237,000,000 KB.
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