The Momentus XT is a curious beast. It actually doesn't reveal its true colors when taxed in standard benchmarks, which makes a longer-term, real-world evaluation of it that much more important. You see, this 500 gigger actually has 4GB of NAND onboard, but given just how small 4GB is in relation to the other 496GB, the drive obviously has to be extra choosy when determining what goes where. Standard benchmarks will prove that a straight-up read / write on this drive is similar to any other 7,200RPM drive of this caliber. Frankly, there's no real gains if you're using the drive to shuffle 30GB files from server to server each day. The whole point of this drive is to make "the little things" snappier in everyday use for the Average Joe / Jane, largely by evaluating what applications consumers use most and then dedicating the NAND for those high-use apps.
Needless to say, there's not really a great benchmark tool out for that kind of work. This all sounds fine and dandy in theory, but the real question is how does it act in practice. We swapped our standard 7,200RPM drive (also 500GB) out for this unit, cloning the contents along the way. Upon boot, we noticed a 1 - 2 second improvement in how long it took to show us a useable desktop; hardly Earth-shattering, but a decent start. From there, we fired up Firefox, Photoshop CS5, Skitch, TweetDeck and iTunes in succession. Again, a 1 - 2 second improvement in total load time. But after using the apps for a bit, we shut our machine down and rebooted, doing the same song and dance all over again. And again. And again. We went through this process four total times, with each one getting a bit quicker when it came to load time. After we'd given it ample opportunity to grasp our preferred flow, we noticed a 6 - 8 second improvement in total load time. That may not sound like a lot, but percentage wise it's hardly worth sneezing at.
So, if booting up apps was quicker, how's about the actual in-app performance? We used Lightroom 2 as our main test bench here, selecting 300 RAW files and waiting as graphical representations of the color balance lit up in the corner. The difference here was striking. On the prior drive, it took a few seconds per image to display graphical elements about any given image; on the Momentus XT, they popped up instantly. One area where we didn't see such a huge increase in performance was during renders; we exported a 32GB iMovie project into a .mov file for easier transport, and the total time for the task to complete was essentially the same on both drives. Granted, we fully expected this type of behavior, but it goes to show that 4GB of NAND won't exactly alter your universe when looking at chores that require lengthy reads and writes.
All told, we'd have a tough time not recommending the Momentus XT, particularly the 500GB version. If you're in no need of that much space, we'd almost recommend saving up for a pure SSD at 256GB or less. But currently, the price difference between this drive and the half-as-big solid state drives makes Seagate's new alternative that much more attractive. We'd also recommend this only for those who are looking for performance gains in the simplest of tasks; opening your email client, sifting through images in Lightroom, switching between the ten apps you have open, etc. Comically enough, this performance-oriented drive best reveals its talents in the most mundane of tasks, but like it or not, that's what the bulk of us are buried in from

