Early Days of the CRT Display
The first cathode-ray tubes first appeared in computers as a form of memory, not as displays (see Williams tubes). It wasn't long before someone realized that they could use even more CRTs to show the contents of that CRT-based memory (as shown in the two computers on the left). Later, designers adapted radar and oscilloscope CRTs to use as primitive graphical displays (vector only, no color), such as those in the SAGE system and the PDP-1. They were rarely used for text at that time.
Photos (clockwise from top): Computer History Museum, MITRE, DEC, Onno Zweers