The current manufacturing technique of a hard drive platters requires a layer of magnetic material to be applied on the platter. It is made of nanometric magnetic particles, which cannot organize themselves in a completely homogenous way. For that reason, on a microscopic level, chunks of that particles have to be used to create bits on which the data will be stored.
Researchers have however discovered that starting by applying a layer of another material, mostly made of sodium chloride, would allow the magnetic particles to organize themselves in a much more homogenous way. With the proper read-write heads, it would be possible to make platters hold 6 times more data, so 3.5" disks could reach a storage capacity of 20 TB.
There will be other problems to solve before this improvement can be introduced in the mass manufacturing process, but the cost of sodium chloride will not be one as you can find it in about any supermarket, where it is simply called "salt".
