Some online disk drive sites are listing a 1TB 2.5-inch Seagate Constellation drive, which shouldn't exist.
Seagate certainly has 1 and 1.5TB small form factor (SFF) drives inside its FreeAgent GoFlex external drives but has not announced such capacities for internally-mounted SFF drive product.
Span lists a drive with a model number of ST91000640NS, saying its is a 1TB Constellation 2.5-inch drive, spinning at 7200rpm with a SATA 600 interface and a 64MB cache. It's yours for £178.60.
The Polish emarket lists it as a 3.5-inch drive though. Seagate's own site has no mention of a drive with this model number.
Just to add to the confusion, Span also lists a 1TB, 3.5-inch Constellation drive with a 6Gbit/s SAS interface, but uses a Seagate 2.5-inch type model number: ST91000640SS.
Our understanding of Seagate model numbers is, going from left to right, that the "ST" means Seagate. The "9" is a form factor ID with 3 meaning 3.5-inch and 9 meaning 2.5-inch. The "1000" is a capacity measure in GB. The "6" is a cache capacity indicator. The "40" is an identifier of some kind and the "NS" is an interface flag standing for nearline storage and indicating a SATA interface. An "SS" value here would stand for a SAS interface.
A 1TB 3.5-inch SATA interface Constellation drive on Seagate's site has a model number of ST31000524NS. Interpreting this gives us a Seagate 3.5-inch model (ST3) with a 1TB capacity, a 32MB cache (the 5 flag we think), for nearline (NS) application use.
This leaves us thinking that either the Polish site or the Span site got the model number or form factor wrong. A 1TB 2.5-inch Constellation is certainly a feasible configuration, as the GoFlex FreeAgent and Western Digital's 1TB, 3-platter Scorpio Blue show.
Also, we reported that Greenbytes was qualifying what looked like a 1TB Constellation back in May. Normally you would expect Seagate to announce such a product with a fanfare and corporate chest-beating.
We asked for confirmation and a Seagate spokesperson said: "We have not announced such a product..." ®