One-inch hard drives began appearing in cutting-edge media players and some smart cell phones almost six months ago. Now they’ve migrated from living inside handheld devices to being available as external, and highly portable, USB devices.

			Contents • Archos ArcDisk • Imation Micro Hard Drive • Seagate Pocket Hard Drive • Sony Micro Vault Pro • Summary

How have we gotten from 5.25 inches to one inch? It's not just a matter of shrinking the component sizes — otherwise, the capacity of hard drives would have shrunk along with their physical dimensions. By the time we hit the one-inch size, the average flash drive would have been more spacious. While there are other factors involved, successfully downsizing the hard disk is basically the result of increasing the areal density, or how much data can be packed into a given square unit of area of one of the drive’s platters.

Currently, by refining the method used to lay down particles on a drive’s platter and the ability to read and write to them, we’re hovering around 100 gigabits per square inch. Yes, those are gigabits — it takes eight of them to make up 1GB (gigabyte) of data. (And it gets more confusing — hard drive manufacturers insist that 1KB is 1,000 bytes while savvy computerists understand that it’s really 1,024 bytes. That’s why rated and actual hard drive capacities never seem to quite agree.)

These one-inch drives have a theoretical maximum of 12GB. What this actually translates down to is about 6GB per platter.

We haven't hit any kind of wall even yet. Technology continues to evolve. Not only are there smaller (0.85-inch) drives in the hopper (not to mention one in this review), but also larger areal densities (at least 138Gb/in²) on the horizon, thanks to the use of vertical (also called perpendicular) recording technology. In current technology, horizontal (or longitudinal) recording, the bits used to record the 1’s and 0’s of digital data are laid out end-to-end on the drive’s platter. In a vertical world, those bits stand up on the platter, side by side, allowing more of them to be packed together. While hard disks are considered a non-volatile (or permanent) storage medium, their design technology is apparently quite volatile.

(You may at this point be asking, "Why not simply use a USB drive (or flash drive, pen drive, keychain drive, key drive or memory key, depending on what you like to call it)?" The key —forgive the pun — is that hard drives are cheaper.)

The pocket pals reviewed in this article are from Archos (4GB), Imation (2GB), Seagate (5GB), and Sony (5GB). All of these drives are powered through the computer’s USB port. Don’t expect them to work from a non-powered USB hub or keyboard. Both of these devices draw power from your PC’s internal USB, where the maximum available power is 500 milliamps (mA). Adding a mechanical device like a hard drive may push you beyond that maximum.

In addition, while each of these drives is capable, in theory, of being used as a boot device, putting that into practice means being able to create a boot partition on the drive and, more importantly, having a computer that will let you boot from a USB device. Not all do.

How We Tested
To test the pocket hard drives, I created three groups of files, each containing three sets of files.

The first group was comprised of Microsoft Word documents in a wide variety of sizes. The first file set in this group contained 4,410 files, the second contained 8,820 files, and the third contained 11,025 files.

The three file sets of the second group consisted of video files: 1.68GB, 3.41GB, and 4.58GB, respectively. The first file set contained two files, the second had four, and the third had five.

The group of music files was composed of 1.75GB, 3.67GB, and 4.51GB MP3 file sets. The total number of files in each music set was greater than the number in each of the video sets, but also well below the count of .doc files in the first group.

Windows Copy and Paste was used to perform the transfers, and timing was done manually using a Heuer stopwatch.