The world's top three hard drive manufacturers agree that 1 Tbit/sq inch hard drives are possible with perpendicular recording technology. 1TB 2.5-inch drives or 5TB 3.5-inch ones could be delivered by 2010.

Seagate, Hitachi GST and Western Digital all confirmed that 1 terabit per square inch areal densities are possible by developing today's perpendicular recording technology. Previously Seagate alone had suggested it might be feasible.

Currently real densities are passing 250 gigabits per square inch. These density levels are driving the introduction of 2.5-inch disk drives, which need less electrical power than mainstream 3.5-inch ones, and are capable of delivering more I/Os from a drive array shelf. For example, Toshiba has a 254.8Gb/sq in-based notebook product offering 320GB of serial ATA (SATA) storage on two platters.

Hitachi GST's CTO, John Best, said: "We now think there's a reasonable chance we will get to a terabit per square inch. That's just my gut feeling. We have not done a thorough technical analysis yet."

Western Digital CTO, Hossein Moghadam, said: "Getting to a terabit per square inch is now seen as possible."

Seagate CTO, Martk Re, was more bullish: "We have some credible ideas for going to at least a terabit with perpendicular."

The top three manufacturers appear to think that 1Tb/sq in drives could be delivered before 2015 after which HAMR technology would be needed to exceed that areal density.

When perpendicular recording technology runs out of steam then the industry will have to invest a large chunk of capital in new technology, currently thought to be heat-assisted magnetic recording (HAMR). Delaying this transition will enable vendors to defer this spending.

This suggests the following timeline:

2007 - 254Gb/sq in meaning a 2-platter 2.5 inch drive can hold 320GB
2011 - 500Gb/sq in resulting in a 640GB 2.5 inch dual platter drive
2015 - 1Tb/sq-inch and a 1.28TB 2-platter 2.5-inch drive with the HAMR technology transition in prospect.

In effect we are looking at a doubling of drive capacity every four years. A rack shelf of forty 2.5-inch drives would hold 25TB by 2011 and 50TB by 2015.

In the 3.5-inch form factor area this would mean a 24TB low-end drive array by 2015. For example, Dell has its current PowerVault MD3000 line of serial-attached SCSI (SAS) 3.5-inch drives. They store up to 6TB of data on 15 3.5-inch drives. The areal density increase time line above would enable a 12TB version of this by 2011 and a 24TB version by 2015.