I remember the first time I learned about hybrid hard drives--models that combine traditional spinning platters with a sizable chunk of solid-state flash memory.

The goal was to combine the best of both storage worlds into one drive: The low cost and high capacity of a hard disk, plus the speed of flash. It sounded like a great idea to me.

Seagate

That was way back in 2006, though--and hybrid drives have never quite taken off. But the concept still makes sense, and hard-disk kingpin Seagate is releasing a new hybrid drive designed to deliver on the technology's promise.

The new Momentus XT is the second-generation version of Seagate's first hybrid drive. (The company says it's sold a million of the original version--not huge numbers, but more than the technology's low profile to date might suggest.)

This updated drive packs both a 750GB 7200rpm conventional drive (50 percent bigger than the maximum capacity of the previous version) and 8GB of NAND flash (twice the previous amount). Seagate technologies called FAST Factor Flash Management, FAST Factor Boot, and Adaptive Memory put frequently accessed data like applications and the operating-system components needed to boot the PC into the flash memory so they'll load quickly. Everything else stays on the spinning disk, which provides more elbow room for files than any consumer solid-state disk.

So why would the new Momentus be more of a mainstream hit than its predecessor? Seagate says that it's 70 percent faster than its earlier hybrid drive and three times quicker than a garden-variety, non-hybrid disk. Its benchmarks for cold boots and application launches show the new drive to be just a few seconds slower than a SSD. Or, in some cases, a few seconds faster.

Seagate

Of course, it's lots of storage at a low price that makes the hybrid proposition intriguing. The 750GB Momentus lists for $245 as an upgrade kit--roughly the same cost as some SSDs with only 120GB of space. (It might have had an even more striking cost advantage, but it's debuting during an ongoing hard-drive shortage, the result of flooding in Thailand, that's driving disk prices up.)

In the end, hybrid drives are compromises, neither as cheap as ordinary drives--you can get a conventional 750GB Momentus for about $150--nor as fast and energy-efficient as SSDs. And they take up as much room as a conventional drive, unlike the solid-state storage that Apple mounts directly on the MacBook Air's motherboard to conserve space and permit a thinner case.

Having lived with a MacBook Air with 256GB of space for the last year--and struggled to keep from filling it to the bursting point--the notion of a reasonably-priced drive that's nearly as fast with almost three times as much space has me interested in hybrid drives all over again.



I expect to live long enough to see SSDs largely replace conventional drives, but it's going to be a long time until they're big enough and inexpensive enough to do so. And until they are, hybrid drives like the Momentus still have a shot at the big time.

