What do the magnets in a hard drive do?
In: Technology
Hard drives store data as magnetic patterns on the surface of a metallic disc. The magnets on the heads of the drive arms read and write those magnetic patterns and the disc spins beneath them. Its a little bit like an old record player, where the needle on the arm reads the pattern on the record. Expect the arm has magnets instead of a needle, and record spins a LOT faster, and the arm does not physically touch the disc.
this only applies to traditional HDD drives – newer SSD (solid state drives) do not use magnets or moving parts
A spinning hard drive has two main components that it uses to store and retrieve data. It has a set of spinning metal platters that house the data, and an arm that moves a read/write head across the platters.
The magnet(s) are used in the arm part. I actually had a disk open on my desk so I took a picture of it. [The hard drive](https://imgur.com/rNINr68). In the picture at the bottom left you can see the arm and the magnet under it. This drive had two magnets, one above and one below, but I removed the top one so you could see the arm. The arm has a coil of wire on it that has electricity run through it to create a magnetic field, this magnetic field interacts with the field from the magnet to move the arm, much like how an electric motor works, but laid out flat. The magnet is very powerful (like crush your fingers powerful) so that the arm can be moved very precisely and very quickly to the correct spot on the disk.
This works a bit like a vinyl record player, except that instead of the arm moving from the outside of the disk to the center slowly, reading the whole disk, the arm will jump back and forth across the disk very quickly moving to where the data is.
I don’t know that the other comments really address what the magnets actually do. So, the idea is that the disk surface is made of a material you can magnetize or de-magnetize on demand (the platter). The heads can selectively magnetize or de-magnetize a very focused small spot on its surface when they write, or report on whether a spot is already magnetized or not when they read. A magnetized spot is a 1, a no magnetized one is a zero.
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