It used to be that you had the primary store, and it was anything from acoustic delaylines filled with mercury via small magnetic dougnuts via transistor flip-flops to dynamic RAM.
And then there were the secondary store, paper tape, magnetic tape, disk drives the size of houses, then the size of washing machines and these days so small that girls get disappointed if think they got hold of something else than the MP3 player you had in your pocket.
And people program this way.
They have variables in “memory” and move data to and from “disk”. [...]
Well, today computers really only have one kind of storage, and it is usually some sort of disk, the operating system and the virtual memory management hardware has converted the RAM to a cache for the disk storage.[...]
Virtual memory was meant to make it easier to program when data was larger than the physical memory, but people have still not caught on.