But a new generation of higher-performance, power-thrifty models has done much to narrow the performance gap.

Western Digital, a major manufacturer of internal and external desktop hard drives - has announced its first foray into mobile hard drives.

If the new drives live up to their promise, they should be among the best options available.

The Scorpio line of drives debuts in 40GB, 60GB, and 80GB capacities.

The drive has a rated average seek time of 12ms, and comes with a 2MB buffer (an upgrade to 8MB is optional).

Like competing high-performance models from manufacturers such as Hitachi Global Storage Technologies and Seagate Technology, Scorpio drives will spin their platters at 5 400rpm.

Such high-speed spinning presents special problems with heat build-up, power use, and sound volume. The company says that it has solved all of these problems.

To keep sound levels low, Western Digital teams its SoftSeek algorithms (which quiet the clicking typical in drive seeks) with its WhisperDrive technology (which includes fluid dynamic bearings and a specially dampened top cover).

The company claims that models in the Scorpio line are the quietest mobile hard drives on the market.

Heat will not be a problem either, according to spokesman Darrin Bulik. "Scorpio has run cooler in our tests than the competing 4 200rpm and 5 400rpm models to which we have compared it," he says.

Energy miser

Aside from heat issues, power consumption is perhaps the biggest concern for notebook computer users.

Western Digital reports that Scorpio drives should be very miserly in their use of energy, taking roughly the same amount of power as 4 200rpm drives while running far faster.

The Scorpios should be hard to squash as well. Each drive comes with a strengthened cover that stands up better to top-down pressure (as might happen if someone were to lean heavily against the notebook's palm rest).

Mobile hard-drive shock resistance has generally improved in recent years, and Scorpio drives are rated to withstand 250Gs while operating and 900Gs of non-operating shock.

The company expects its DuraStep Ramp technology to enable the drive to perform at least 600 000 load/unload cycles without contaminating the drive's clean internal atmosphere.

The drives began shipping in volume to notebook manufacturers today, and they should be available to notebook buyers within the next month or so, Bulik says.

He declines to name notebook vendors that will be selling models incorporating Scorpio drives, though he does say that the drives are in qualification with all of the top ten vendors, among others.

With the market growing at about 20% annually, according to industry research analysis firm TrendFocus, demand for mobile hard drives is increasing.

Western Digital's customers have been urging the company to offer mobile drives, says Bulik. With their strong resume, Scorpio drives are likely to thrive under these conditions, he concludes.