Punched Cards to Core Memory
The history of memory is a history of making the invisible reliable.
Punched cards made data portable and repeatable, but they were slow to read and awkward to change. Magnetic core memory offered something different: fast, random access to values held inside the machine. Each core stored a single bit as a direction of magnetization, and a plane of cores became a tiny, intricate grid of state.
Core memory was expensive and hand-assembled, but it was dependable enough to become the standard for a generation of computers. Its decline came with semiconductor memory, which was cheaper and denser. The underlying idea, however, remained the same: a machine needs a fast, addressable place to hold the values it is working with.