Fujitsu is working on patterned media technology, which could pave the way to 5TB desktop HDDs and 1.5TB notebook HDDs in the not too distant future.
Fujitsu was not able to comment on the track width of the hard drives in production today, but mentioned that the technology would allow storage density to climb to about 1 Tb/inch2 - more than five times the density that is available in production hard drives today. This density corresponds to what most hard drive manufacturers consider to be "superparamagnetic" limit for the recently introduced perpendicular magnetic recording technology (PMR). The current storage density record is held by Seagate, which claimed in September of last year the development of a storage device with 421 Gb/inch2 storage density.
In theory hard drive makers could reach at least a density of 1 terabit per square inch with patterned media, some physicists even claim densities of up to 20-40Tb/inch² will be possible in the future.
The conservative guesstimates of 1Tb/inch² translates to 5TB for 3.5" desktop HDDs, 1.5TB for 2.5" notebook drives and 500GB for 1.8" HDDs for portable media players.