The days of 4MB drives being massive are long passed, thankfully, and now we're breaking into new hard drive capacity territory. Despite the HDD industry's slow recovery speed, Hitachi has shipped its most recent Deskstar 5K, a 4TB HDD that runs at 5900RPM (dubbed the 'CoolSpin' by Hitachi), 32MB of cache, and a SATA III interface (6Gb/s max bandwidth).
The slower RPM should encourage stability (which has been notoriously destructive on larger drives) and lower power consumption. Generally speaking, large drives are meant solely to be storage drives -- not performance drives. Of course, if you wanted to buy one of these, our hardware experts would recommend running a mirrored RAID configuration in the event of a catastrophic failure. You really don't want to lose 4TB worth of data.
Hitachi's Deskstar 5K (model #HDS5C4040ALE630) has been spotted in Japan and has not yet been seen on US retailer online locations (please comment below if you spot it!). Judging by the ~¥27,000 price-point, we'd expect the drive to rank somewhere in the $300 to $400 range in the US. Quite expensive. The sad thing? Artificially-inflated drive prices due to flooding in Thailand make this drive a much better value than the $100 500GB drives you see out there currently. Things will improve soon enough.
Image Source: Akiba (translated from Japanese)