The goal is to increase the maximum storage density of a technology that is, in its very basics, almost 40 years old.
About 20 years ago, the industry believed that traditional horizontal magnetic recording techniques would top out at a density of about 100 Gb/square inch. 15 years ago, Seagate began experimenting with heat-assisted recording technology acquired with Quinta, which promised up to 250 Gb/square inch, but was able to push the boundaries up to 250 Gb/square inch in regular magnetic recording -- until the current perpendicular magnetic recording (PMR) arrived in 2006, which is now believed to take the industry just over 1 Tb/ square inch.
Seagate, for example, is working on heat-assisted magnetic recording again, but there may be another opportunity: Grain-based magnetic recording, which apparently allows up to 10 Tb/square inch. In more common terms, this would enable hard drives in the range of up to 50 TB for 3.5-inch models.
According to an article over at X-bit labs, this technology would be "storing each data bit in a single magnetic grain of the thin film of the recording medium, rather than in several grains as in conventional hard drives". Initial test results at the A*Star Data Storage Institute appear to be encouraging and are good enough to be considered for a future magnetic recording type, which could enable the industry to elude, once again, the rather expensive move to heat- or laser-assisted magnetic recording.