The Register has learned that Seagate will introduce a 3TB HDD sometime within the year. Based on information provided by unnamed sources "familiar with the company's plans," The Register claims that the upcoming storage beast will be part of Seagate's Constellation ES enterprise-class line, and will feature a 6Gbit/s SAS interface.
According to Seagate, the Constellation ES line serves as a replacement for the Barracuda ES series. The largest Constellation ES drive to date is the 3.5-inch 2TB model spinning (round like a record baby) at 7,200rpm.
On the 2.5-inch front, the Constellation ES line maxes out at 500 GB capacity. However Seagate will supposedly release a 1 TB 2.5-inch model in June or sometime thereafter, making it the world's highest-capacity 2.5-inch drive until Toshiba, WD or another manufacturer comes along and takes the crown.
On a related note, The Register also learned that a new Savvio 2.5-inch drive is on the way, building upon the current 10K.4, 10,000rpm drive capacity limit of 600GB. This new HDD may offer a storage capacity of 750GB, however the exact amount is currently unknown.