In 1950s they were shrinking vacuum tubes, making them smaller and smaller. They finally hit a wall; they couldn't shrink the vacuum tube any more and keep the vacuum.
在50年代，工程师们都为尽可能地 缩小真空管而努力。但最终碰了壁。 他们无法继续缩小真空管并同时保持着真空的状态。