Mercury delay lines were a form of memory that predates and is distinct from plated wire memory. Plated wire memory is magnet memory, like core memory, but with

Mercury delay lines were a form of memory that predates and is distinct from plated wire memory. Plated wire memory is magnet memory, like core memory, but with permalloy coated wires rather than little permalloy donuts like the elements of core memory. Delay line memory uses a transducer that puts vibrations into a medium in a tube (mercury) that travel the length of the tube at the speed of sound through that medium (1450 m/s) a transducer at the other end picks up the vibrations and decodes them back into bits. While the signals are being sent down the tube they are "in memory". By sending the signals back to the beginning of the tube a set of bits can be kept recycling indefinitely (120 bits per delay line in the UNIVAC I). The UNIVAC I only had 1000 thirty-five bit words in its memory. These were store in a set of these mercury delay lines. In my first digital design lab course at MIT there were a few old delay line memories kicking around which I briefly considered using for a project. I ended up needing only 5 shift registers of around 6 bits each so I just used flip flops to build them for the nim-playing computer I built.