The drives
With the exception of perpendicular recording technology, mobile ATA drives don't differ much from one another when it comes to major features. They do differ in other respects, which we've outlined in a handy comparison chart that includes all the drives we're comparing today. The Hitachi Travelstars, Seagate Momentus drives, and Western Digital Scorpio we've assembled represent the best each manufacturer has to offer the 2.5" mobile ATA space. Fujitsu's MHV2040AT is far from a flagship product, though. It's a drive we purchased to represent what most folks will find lurking inside their laptops—a low-end model lacking in cache, capacity, and spindle speed.

The table below is comprised of manufacturer-supplied specifications, so keep that in mind. We will test real-world transfer rates, power consumption, noise levels, and the like in the following pages.

Although desktop ATA drives that support 133 MB/s external transfer rates have been available for some time, laptop drives have stuck with 100 MB/s. That shouldn't be a big hindrance considering that even high-end SCSI drives have a hard time sustaining transfer rates above 100 MB/s, but it could slow the burst performance as drives serve data directly from cache. Cache size is another area where these laptop drives are a step behind their desktop counterparts. While 16 MB of cache has become common on even mid-range desktop drives, all but one of our mobile drives is equipped with 8 MB of cache. The exception is Fujitsu's MHV2040AT, whose 2 MB cache is typical of the kinds of low-end drives found in most laptops.

The MHV2040AT's lowly 4,200-RPM spindle speed also sets it apart from the pack, as the rest of the drives we've assembled spin at 5,400 or 7,200 RPM. Both Hitachi and Seagate offer drives with faster 7,200-RPM spindle speeds, but Western Digital's Scorpio is 5,400 RPM-only, so don't expect it to match the fastest Momentus and Travelstar drives.

While hard drive manufacturers all agree on how to represent their drives' spindle speeds and cache sizes, expressing drive performance is another story. Some manufacturers prefer to publish an average sustained transfer rate taken from the middle of the disk, while others choose to reveal their drives' media transfer rate, which is the highest transfer rate along the densest outer edge of the disk. Obviously, the media transfer rate is more of a best-case scenario, making it difficult to compare expected transfer rates from different hard drive manufacturers. Note that drive capacity can also affect the media transfer rate, as we see with the Travelstars. This is due to the fact that different capacities can use platters with different areal densities, with the denser platters providing speedier transfer rates because the drive head can access a greater amount of data over a shorter physical distance.

In addition to disagreeing over which transfer rate specs to publish, hard drive manufacturers also differ when it comes to revealing seek times. Some prefer to separate seek times into read and write components, while others simply report an average seek time. Here, spindle speed reigns supreme, although it's interesting to note that Seagate's average seek times are half a millisecond short of those reported by Hitachi and Western Digital, even when spindle speeds and rotational latencies are equal.

There's little variance in the acoustic and power consumption specs published by each drive manufacturer, and given the relatively low noise levels and wattages, that's not surprising. We'll be doing our own noise and power consumption tests to see how the drives shake out in the real world.

Unfortunately, we can't adequately test the reliability of each drive in the real world. Well, we could, but you'd be reading this comparison several years from now, so it wouldn't be all that topical. Still, the warranty length offered by each drive manufacturer at least tells us how long users will be entitled to a free replacement drive in the event of a catastrophic hardware failure. Seagate is king here, offering five years of coverage on all its mobile (and desktop) hard drive products. Three years is pretty standard for the rest of the field, although Western Digital's policy of only offering a single year of warranty coverage with retail drive kits is a bit puzzling. If anything, one would expect bare drives to be covered by a shorter warranty.

With varying spindle speeds and capacities, it's no surprise that the drives we'll be looking at today are all over the map when it comes to pricing. As expected, the Fujitsu MHV2040AT is the cheapest of the lot. It's a little jarring that the perpendicular Momentus 5400.3 is so much more expensive than even 7,200-RPM drives, but industry-leading capacities have always commanded a hefty price premium.

Since mobile drives aren't all that visually stunning, we'll make do with a group shot of all the drives. As you can see, they look pretty much identical.