Western Digital has bumped up the capacity of its two-platter SATA drives to 640GB, an increase of almost a third, and is planning more drives based on its latest 160/320GB disk technology.

The new 640GB Caviar SE16 drive, which lists for £85, follows on from a single-platter 320GB model. WD said that it offers a 3Gbit/s data transfer rate, spins at 7200 RPM, and has 16MB of cache memory.

Although it might look like a 320 with an extra platter - and indeed, the platters and heads are the same - the 640GB drive is actually a separate product with some new parts, such as the motor, said Ted Deffenbaugh, WD's senior director of product marketing.

He explained that single-platter drives are aimed at the entry level market, where "acoustics are critical", so they are tweaked to run almost silently at the expense of a little performance. Two and three-platter drives are "more performance-optimised, even though that means a bit more seek noise."

The 320GB platters could also be used in single-sided form to produce a 160GB drive, targeting what's now the sweetspot for the mass market, Deffenbaugh said.

"We are going to see phenomenal economies of scale from this," he predicted.

He added that it could also be possible to squeeze a bit more capacity out of the platters and build a three-disk 1TB drive, but refused to say if or when that might reach the market.

Deffenbaugh acknowledged that 640GB is a rather unusual capacity point, and said he doesn't expect to sell too many to commercial desktop buyers.

"Businesses sometimes get nervous if the capacity looks too large - it looks like it's screaming out for media content," he added.

But he pointed out that for those buyers who do want capacity, the new drive offers 28 percent more than the 500GB two-platter drives that the rest of the industry is promoting, yet costs little extra.