The Seagate Momentus XT combines traditional spinning storage technology with non volatile silicon-based flash memory in an attempt to get the best of both worlds, ultra fast access and massive capacity at an affordable price.
Just as some current processors come with three levels of cache for optimal performance, the Momentus XT drive has three different storage packed in one; there's a 32MB buffer, then 4GB onboard SLC flash (not MLC) and finally 500GB capacity on the model we tested.
Note that Seagate doesn't quote their hard disk drives as sporting the additional 4GB storage but instead labels it as "Adaptive Memory", one which automatically adjusts its performance to suit the users' needs by monitoring "your frequently used applications and data files, then placing them into the solid-state portion of the drive so that they can be recalled quickly".
In a nutshell, it looks a lot like what Windows' Readyboost does but is OS, driver and software independent (ed : it would be interesting to find out what would happen if the Momentus XT was combined with Readyboost).
It also means that improved performance can only be obtained over time rather than straight out of the box as the algorithm "learns" the user's habits; which is the opposite of what you'd expect from SSD technology.
It has a SATA 3Gbps interface with NCQ, something you have to bear in mind should you want to upgrade your existing storage solution. The model we tested, ST95005620AS, has an areal density of 394Gb per square inch which is significantly less than the 541Gb per square inch that the biggest Momentus member (a 750GB model) sports; in other words, there's room for the XT's capacity to grow.
Available in 250GB, 320GB and 500GB capacities, the cheapest Momentus XT costs around £71 while the most expensive model, with double the capacity, is around £25 dearer, significantly less than the suggested retail price of £109+VAT. It is also more than twice the value of an entry level 500GB 2.5-inch hard disk drive like the Western Digital Scorpio Blue (although this one has only 8MB buffer and spins at 5400RPM).
As expected, the drive is 9.5mm thick which makes it compatible with the overwhelming majority of laptops, netbooks and portable hard disk drive enclosures out there. In our subjective tests, we found out that Adaptive Memory performs as expected, especially after a few runs; our test system booted faster, application starts were quicker and most importantly, the drive is supported by all major operating systems.
Seagate quotes an average read/write seek time of 11ms and 13ms respectively with an I/O data transfer rate of 300MB per seconds. Importantly, the average seek power is 2.2w only with the operating power consumption being half that. This means that heat dissipation and acoustics are minimal; the drive was warm to the touch under normal operaing conditions and was whisper quiet.
The Momentus XT also comes with a five year warranty which comes in handy as Seagate expects around one in every 200 drives to fail each each year. We think that Seagate has an innovative technology in the offing but that it doesn't push it far enough, possibly because of technical and cost constraints.
It does however open the tantalising prospects of a 2011 version of the XT with a 750GB platter (as for the ST9750420AS), coupled with SATA 6Gbps interface, twice the memory buffer and a much bigger onboard flash capacity to offer more leeway to the algorithm. Getting two of those in RAID-0 should beat the average SSD while offering significantly more storage capacity.
It will also be interesting to see whether Seagate rolls out Hybrid drives on its desktop models as well in a near future especially on enterprise ones like the 15K Savvio or the Cheetah drives - now that would be tasty. Alternatively, Seagate could use it to boost performance at the lower end of the spectrum without increasing spinning speed or heat dissipation.
As for the bottom line, well, Seagate has, in the Momentus XT, a winner, the fastest 2.5-inch hard disk drive on the market, one which will be at ease both in a portable environment and in a data centre. Ultimately, it is a hybrid storage solution, one that offers significant gains under the right circumstances.
However, if you can afford to run TWO hard disk drives in one configuration (e.g. in a HTPC or in a DTR laptop), then it may be worth investigating RAIDing two traditional 500GB 2.5-inch hard disk drives instead which could cost less and provide you with better performance and more space immediately.
Find out more about the Momentus XT on Seagate's pages here and here. As a last word, though, we were astonished to see that out of the 30 or so shops that list the Seagate Momentus XT drive we tested, no one, apart from Insight, had it in stock.