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Date: Wed, 29 Mar 2000 10:16:07 -0800 (PST)
Date: Thu, 16 Mar 2000 10:53:38 -0800 (PST)
From: John Nagle
Dead medium: Mechanical Memories (rotating disk, movable pins)
Source(s): personal observation

Bradly O'Neill wrote: "Built by A.D. Booth in post-WWII, mechanical memory "(...) consisted of a series of rotating disks, each of which contained a tiny pin which was allowed to slide back and forth through the hole, and as the disk rotated, a solenoid was used to push the pins so that they protruded from one side of the disk or the other."

Mechanisms like that date back much further than post-WWII. They were a common storage mechanism in jukeboxes back to the 1920s. The oldest one I know of is a destination-sign controller in the London Transport Museum, London. This device consists of a 4-bit rotary encoder, a 4 bit x 10 shift register, and a 1 out of 16 decoder. But it's all 19th century technology. The shift register is a drum with pins, and it's huge; the thing looks like a drive system for a tower clock, standing about three feet high and powered by a weight, cable, and crank, just like a big clock.

As of 1985, it was still working.

John Nagle