Seagate has crammed 1.5TB in the 2.5-inch external drive format with its latest FreeAgent GoFlex model, meaning you can watch 60 high-definition movies one after the other.

Seagate hasn't said if the drive is a 3-platter job, meaning an outstanding but unlikely 500GB/platter, or a 4-platter one, meaning a more reasonable 375GB/platter. Toshiba has a 2-platter notebook drive with 375GB/platter areal density. Seagate also has a 750GB Momentus 2.5-inch product with the same areal density, spinning at 7200rpm. Perhaps it is a 4-platter version of that product? We have asked Seagate the question but haven't heard back yet.

The achievement of a 1.5TB capacity in this form factor gives Seagate retailer and e-tailer shelf leadership and should help prod Hitachi GST, Toshiba and Western Digital into following suit.

The product comes with a USB 3.0 cable which is backwards compatible with USB 2.0 ports. From now on all GoFlex external drives will ship with such a cable. Seagate suggests that the drive can transfer a 25GB file in under five minutes versus the 14 minutes it would take using a traditional USB 2.0 drive; basing this on an average transfer rate of 30MB/sec for USB 2.0 and 100MB/sec for USB 3.0.

This drive can be used with an array of add-on cables such as eSATA and FireWire 800, and accessories such as the GoFlex Net media sharing device and the GoFlex TV HD media player. Its enclosure has the same dimensions as the previous 750GB and 1TB models.

The 1.5TB GoFlex is available in the USA today, in black only, and can be bought for $249.99. It will be available outside the US by the year end.

Update: Seagate confirmed it is a 4-platter drive with 375GB per platter and a rotation speed of 5400rpm. ®