So far, the vacuum tube computer has consisted only of the central processor: arithmetic and logic unit, instruction decoder, and control logic. Now it’s time to give it some memory—a whole two bytes of it—built from bistable flip-flops using a clever circuit with 6AU6 tubes and a type 6977 triode vacuum fluorescent display.
Even vacuum tube computers back in the 1950s didn’t use vacuum tubes for their main memory, relying on mercury delay lines, magnetic drums, core memory, or other technologies, so this is more akin to the registers of those computers than their main storage. This memory is purely for data—instructions for the computer will not be stored in memory but rather read from a device like magnetic tape, acting like the read-only memory of an industrial microcontroller today.