Why did magnetic-core memory become an important form of main memory in the 1950s?

Magnetic-core memory became the principal form of main memory in the 1950s primarily because it was the first relatively cheap random-access memory (RAM) device.12

Before its development around 1952, computers relied on less efficient or more complex technologies, such as mercury delay lines, cathode-ray tubes, or magnetic drums. Unlike serial access memory—where data must be read in a specific sequence—RAM allows storage cells to be accessed directly for read and write operations, providing a significant performance advantage.23

The technology consisted of an array of tiny, doughnut-shaped ferrite magnets threaded onto a grid of wires. By directing current through these wires, the magnetic alignment of individual cores could be changed to represent binary values of 0 or 1. This reliable and cost-effective design remained the standard for main memory until it was eventually superseded by semiconductor memory in the late 1960s and 1970s.214