The transistor revolutionized the world and made the abundant computing we now rely on a possibility, but before the transistor, there was the vacuum tube. Large, hot, power hungry, and prone to failure, vacuum tubes are a now-forgotten relic of the very earliest days of computing. But there's a chance that vacuum tube technology could make its way back into computers—albeit without the vacuum—thanks to NASA research that has put together nanoscale "vacuum channel" transistors that can switch at more than 400GHz.
Vacuum tubes have three important components: two electrodes—the negative, electron-emitting cathode, and the positive, electron-receiving anode—and a control grid placed between them. The flow of current between the cathode and the anode is controlled by the grid; the higher the voltage applied to the grid, the greater the amount of current that can flow between them. All three parts are housed in an evacuated glass tube or bulb and look somewhat like a kind of overcomplicated light bulb.