Williams tube – cathode ray tube used as computer memory
The early days of electronic computing involved desperate attempts like this to build a fast temporary storage device. Things were in better shape on the arithmetic and control side - tubes worked, although it took some time to get component reliability up to an acceptable level.  ENIAC, Colossus, and the IBM 603 Multiplier all had very limited memory, under 100 numbers.<p>This was a huge problem for anything that needed even a little storage. Western Union built Plan 55-A, a message switching system for telegrams, sort of like Sendmail.  The buffering was all paper tape punches feeding paper tape readers.  This was slow, expensive, and required large buildings full of paper tape gear and a huge staff.  This was used from 1948 to 1976.  The whole network of US paper tape gear switching centers was then replaced by one mainframe computer.<p>Today, we think nothing of software that needs a few gigabytes to display a text message.