It was an easy prediction, and not surprisingly, it came to pass: Perpendicular recording now enables drive manufacturers to bring typical desktop drive capacities to high-end laptops.

Experienced readers understand the concept of perpendicular recording, but a simple explanation will help those who haven't followed the technology's development: A disk platter contains magnetic bits, which traditionally had lain horizontally upon its surface. Perpendicular magnetic bits, on the other hand, are placed vertically, an arrangement that allows them to consume less surface area, albeit with a thicker surface. Reducing surface space per bit allows more bits per square area, thus, greater per-platter capacities.

Greater platter density also allows a greater number of bits to pass under the head per revolution, which could mean significantly higher transfer rates. But narrower tracks can make it harder for the heads to locate the correct track quickly, so we wouldn't expect first-generation drives to run at the highest available rotational speeds. A balance of slower rotational speed and higher density could still provide these high-capacity drives with similar transfer performance to their high RPM counterparts -- along with all the benefits of a tinier, less-power-hungry form factor, which will improve notebook battery life.

The first 2.5-inch perpendicular drive to reach us is Seagate's Momentus 5400.3, offering up to 160GB capacity via two 80GB platters. We'll be examining the trade-off in speed for capacity, and deciding whether, given the price premium on new technology, the drive can live up to the performance, quality, and value expected for its presumably high-end mobile market.