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It's been a while, so I went to Wikipedia for a refresher. These things really are amazing.

https://en.wikipedia.org/wiki/Storage_tube#Storage

Unlike a television CRT, the storage tube will "remember" everywhere the electron beam struck the screen as long as the voltage is below the erase threshold.

What's wild is that this information can be read back out of the device. So, it's not just a display but also memory. It's a destructive reading process (not unlike core memory) where detection is also erasure, but it really is RAM... of a sort.