Labs

External hard disks

This month's 13 hard disks all serve the same basic function, but they're not all alike. Since seven of them are designed to be portable, while the other six are for the desktop, we've scored them according to different criteria. Each drive is awarded a score out of six for performance, features and design and value for money, as well as an overall score, but these scores are only comparable to drives of the same type. For example, three portable disks achieve top marks for performance, but that merely means they're the fastest of their type in this Labs. In fact, several desktop drives are faster.

Performance

Though physical specifications vary, in practice what's important is how quickly each drive reads and writes files. First, we connect the drive via USB 2 to a PC running Windows Vista and format it to NTFS. We then use Windows Explorer to copy a single 50MB file from a RAM disk onto the drive, timing the operation from start to finish. We then dismount the drive (to prevent Windows' file caching service affecting the results), reconnect it and time the same operation in reverse. This is repeated five times for each drive, and five times again for those with eSATA.

We then repeat the exercise using not a single file, but a folder containing 500 assorted small files, totalling 50MB. This gives an indication of how each device copes with the overheads of the Windows file system. The stars we award reflect the best speed available from each drive, so the highest marks in the desktop category go to those with eSATA support.

Features & Design

Stars for features and design are awarded based on a series of criteria which differs depending on the intended role of each group of disks. For desktop devices, we're looking for a design that will sit on your desk without being obtrusive. We also hope to see conveniences such as a power switch, and ideally a Kensington security slot.

Portable disks tend to sacrifice features in favour of compactness. Here, we look at things like access lights, whether it uses standard cables and how easily it will fit into an arbitrarily arranged workspace.

For all types of drive, we naturally also take capacity into account, as well as aesthetic considerations.

Value for Money

Our value for money score reflects the purchase price of each drive, but we look more at exactly what you get for your money. We calculate what each drive costs in terms of pence-per-gigabyte. Then, we factor in scores for performance and features and design to arrive at a final rating, comparable with the other drives of its type.

Overall

Finally, we derive an overall rating from the average of the other three scores, although due to rounding it may be higher or lower than expected.