Most ultrabooks feature solid-state storage exclusively. Not all of them do, though. Notable exceptions to the rule include Acer's Aspire S3, which couples a 320GB hard drive with a 20GB cache SSD. For systems along the same lines, Western Digital says it's begun shipping a new 2.5" Scorpio Blue hard drive with a slim, 7-mm profile. That's slightly thinner than other 2.5" hard drives, which are typically 9.5 mm thick, and it ought to make the drive more suitable for ultra-slim ultrabooks. WD notes, however, that the new Scorpio Blue remains compatible with drive bays designed for the standard, 9.5 mm thickness.
The new Scorpio Blue is available with 320GB and 500GB capacities, both achieved with a single platter, and priced at $79.99 and $99.99, respectively. Features include "best-in-class" 400G shock tolerance, "the lowest power consumption on the market today" (according to WD), and a two-year limited warranty.
It's still hard to beat mechanical storage when it comes to gigabytes per dollar—you can consider yourself lucky if you find a sub-$100 SSD with a capacity much greater than 64GB. Still, I don't know if I'd make that compromise in an ultrabook. The silence, shock tolerance, and sheer speed of SSDs are all too tempting, even if they call for some belt-tightening on the capacity front.