Ferroelectric densities of .2 to .5 Petabits = 200 to 500 Terabits sq. in. / 40 Petabits = 40,000 to 100 Petabits = 100,000 Terabits cu.cm. or 200,000 to 500,000 Gigabits sq.in. / 40,000,000 to 100,000,000 Gigabits cu.cm. with symmetrical read / write times of < 160 picoseconds for 100 year non-volatile storage having infinite rewrites.
Normally the 1.3 to 5 nanometer molecule can switch at < 160 picoseconds while maintaining non-destructive readout of ferroelectric bistable properties at a 5 nanometer cell size.
This is not the end by any means as Tohoku says their target is 4 Petabits a sq. in or 375,000 Terabits cu. cm. using a .4 nanometer cell size.
Ferromagnetic - Magnetic disk drive have the next highest density at 50 Terabits sq. cm., The Super Paramagnetic Limit. This density is a particle size prediction ( 10 nm ) where the real operational density is more around 1 Terabits sq. cm. as 50 nanoparticles are needed per 1 data bit cell ( ~ 500 nm ). Perpendicular orientation recording will only delay this dead end a few years at most.
Colossal Storage will not use complex wiring schemes that have impedance, heat, and reliability problems but instead will exceed any storage devices proposed and would enable a storage density of more than 100,000 terabits per cubic centimeter. A ferroelectric storage drive device the size of an iPod nano or 3.5 inch drive could hold enough MP3 music to play for 300,000 years without repeating a song or enough DVD quality video to play movies for 10,000 years without repetition.
The only rub is the cost per bit will be cheaper, faster to access, and faster to store for a much longer time unaffected by many environmental conditions.