Puzzler...

Last week's puzzler:

It seems like forever since I posted the last puzzler, about a strange early form of main memory for digital computers.

The correct answer was “mercury”, which got 41% of the 98 votes on this puzzler. To the best of my knowledge, none of the other elements figured in any early computer memory system, though silicon of course is the main constituent of current memory systems.

As one commenter noted, mercury was used in an early memory system that was essentially an acoustic delay line. The system that I worked on used long glass tubes of mercury, bent into a spiral much like a fully compressed spring. Each tube was about three-quarters of an inch in diameter, bent into a spiral that was about six inches in diameter and about four feet long. That means that the tubes, if fully extended, would have been about 100 feet long. The glass was coated with a soft plastic coating that was intended, I think, to provide some high-frequency acoustic isolation. The system had something like 40 of these tubes, providing a 30 bit word with error correction (the extra 10 or so bits). I can't remember some of the interesting details, such as the acoustic frequency or the number of bits held in each delay line. I do remember the main maintenance issue: thermal control. The operation of the system depended on (for those days) very tightly controlled, steady and even, temperatures across the entire array of tubes – not an easy thing to do.

This week's puzzler:

For this week's puzzler, I'm going back to history – this time, a little piece of American history that I happened to witness while I was serving in the U.S. Navy. As always, no fair Googling until you answer!