A great video about disk technology: https://www.youtube.com/watch?v=wtdnatmVdIg.

A snapshot of the disk and its magnets

One of the backbone of today’s technology is the design of hard disks that store data persistently. Before having disks, our “data” must be stored on paper, by ink. Now, those data are persistently stored in trillions of mini-magnets arranged inside a disk, using pure physics. Every time I think about it, I fail to wrap my head around how that became possible, because there are so many crucial details that must be done highly precisely to make it work. The fact that the disk rotates at a constant speed of a few rounds per minutes, to the fact that there is a needle that is just exactly a few nanometers away from the magnets (organized in tracks and sectors) to sense and manipulate the electromagnetic thingy of those magnets, to the electric board to make sense of all those electric signals. And that is the mere thing that empower the data storage in computers, smartphones, autonomous cars, rockets, and spaceships. Wow, just wow.