Hard disk drives store data by changing polarity of cells on the disk platter. Smaller cells are most likely to change polarity and turn unstable which will cause read/write errors. The ability of cells to retain the charge they have been set with is called coercivity. HAMR is aimed at the coercivity increase.
Seagate demonstrated HAMR on a 2.5”, 10000-rpm HDD. However this was only a prototype. Manufacturing of HAMR HDDs will start in 2016. Data density of current hard drives is 750 Gb per square inch. Seagate believes that data density of hard drives based on the new technology will reach 1 Tb and in 2020 it will be 5 Tb. This will enable manufacturers to produce 20TB HDDs.
Implementation of this technology will take a lot of time and effort. Seagate engineers report that all things the most difficult will be adjust a laser to the write head and to implement near-field optics to deliver the heat.