The biggest success story in the hardware world – the 20-to-40 percent gains in hard-drive capacity that manufacturers have achieved each year since the early 1990s – has threatened to end abruptly as engineers run up against a physical limit on the number of individual bits that can fit on a magnetic disk.
Now a new hard-drive technology, “perpendicular magnetic recording,” being rolled out by Toshiba, Hitachi, and some other companies, promises to buy the industry at least a few more years of progress. It will soon allow users of laptops and handhelds to tote around unheard-of amounts of data, while at the same time hastening the demise of “longitudinal” recording, the method used on hard drives since their inception in the 1950s.
In May 2005, Toshiba introduced the first consumer drive incorporating perpendicular magnetic recording: a 1.8-inch, 40-gigabyte drive used in its Gigabeat MP3 player. Now the company is upping the ante with a 2.5-inch drive that holds five times as much data – a full 200 gigabytes. Introduced at this week’s Computex convention in Taipei, Taiwan, the drive is intended for laptop computers, which today typically come with hard drives no larger than 100 gigabytes. Meanwhile, Hitachi unveiled a 2.5-inch, 160-gigabyte drive with perpendicular recording a few weeks earlier, on May 15.
“We’ve been working on perpendicular recording for a very long time,” says John Best, chief technologist at the main laboratory of Hitachi’s Global Storage Technology Division in San Jose, CA. “We saw it as the thing that could keep [hard drive] density moving forward as longitudinal recording was nearing the end of its extendibility.”
On a traditional longitudinal drive, individual bits – clusters of metal grains that encode a 1 if magnetized in one direction, a 0 in the other – are laid down flat on the disk surface. The problem with this approach is that the only way to increase the density of bits on a drive is to make the bits themselves – and the crystalline magnetic grains that make them up – smaller. Below a certain size, however, a grain’s magnetic charge becomes unstable, and can be “flipped” simply by small changes in temperature (a phenomenon called the “superparamagnetic effect”). And if enough grains flip, a 0 might change to a 1 or vice versa, endangering data integrity.
In perpendicular magnetic recording, by contrast, the bits are stacked on end, and therefore can be crammed much more tightly. (For a goofy but entertaining animated cartoon from Hitachi explaining the concept, click here.) That means engineers not only can fit more bits into the same space, but, for a number of technical reasons, can also continue to make bits smaller.