I forgot to mention the amazing plasma technology invented at University of Illinois for the Plato project. <https://ece.illinois.edu/newsroom/article/9931> First, lets think of a neon tube. It gets turned on when a high voltage is applied. With no voltage, no light. But once it has started, an intermediate voltage can maintain the light. If it hasn't started, that voltage will leave the tube off. So, powered by that voltage, the tube is a memory. You can tell its state by the amount of current it draws. Same with pixels on a plasma display. So each pixel is its own memory and no refresh is needed. I first saw a Plato terminal when CDC (a mainframe computer company which had commercial rights to Plato) loaned a few Plato terminals to University of Waterloo for a summer (1972?). (Some old devices did use neon tubes as memories (and not displays). One bit per tube. One example: the IBM 407 accounting machine.) These things were way in advance of other technology. I don't know why they didn't take over the world. Perhaps they were expensive. ================ Another technology that I did not mentioned: Williams Tube memories. These are CRTs but they were used as memories, not displays. So they are a bit off topic.