[rootbear]

As I've studied the history of the early first generation computers, this problem became increasingly clear. Computers were held back by the need for a main memory that was reasonably fast, reliable and affordable at the size needed. Magnetic core was a godsend. Some of the first computers I used had core memories and I have sometimes said to younger coworkers that I got into computers when individual bits were big enough to see.

Others have mentioned that with Williams tubes, you could actually see the memory. That wasn't always the case, as not all Williams tubes had phosphor faces. A tube with a phosphor face was sometimes wired in parallel with the Williams tube to provide a visible copy of the data. The Wikipedia article on Williams tubes explains this:

https://en.wikipedia.org/wiki/Williams_tube