Superparamagnetism sets a limit on the storage density of hard disk drives due to the minimum size of particles that can be used. This limit on areal-density is known as the superparamagnetic limit.
* Older hard disk technology uses longitudinal recording. It has an estimated limit of 100 to 200 Gbit/in.
* Current hard disk technology uses perpendicular recording.  drives with densities of approximately 1 Tbit/in are available commercially. This is at the limit for conventional magnetic recording that was predicted in 1999.
* Future hard disk technologies currently in development include: heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR), which use materials that are stable at much smaller sizes. They require localized heating or microwave excitation before the magnetic orientation of a bit can be changed. Bit-patterned recording (BPR) avoids the use of fine-grained media and is another possibility. In addition, magnetic recording technologies based on topological distortions of the magnetization, known as skyrmions, have been proposed.