One of the laws of computing is that there is never enough disk space — even though today’s PCs have storage capacities that would have seemed impressive for a corporate data centre a couple of decades ago. And the technology that has made these multi-gigabyte drives possible is running out of steam — just as the demand is growing to put disk drives in ever-smaller devices, such as smart phones.We are nearing the physical limits of how many bits can be packed onto a magnetic surface. To feed the seemingly endless appetite for storage, we need something new. That something new seems to be, in a sense, something old.
The answer to cramming in more data appears to be perpendicular recording.
All magnets have a polarization — north pole at one end, south at the other. Bits on a disk are the same. These bits are aligned parallel to the disk surface — that is, if you think of the bits as cars, where the north pole is the front and the south pole the back, they’re parked bumper to bumper.
Now just as right-angle parking lets you get more cars along a stretch of curb, perpendicular recording lets more bits fit on a given amount of disk surface.
In the disk’s case there’s more to it than that. Up to now, disk makers squeezed in more bits by making the bits smaller. But when the bits get small enough, they start interfering with each other through a process called superparamagnetism, or “flipped bits.” When the bits are turned perpendicular to the disk surface, flipped bits are less likely.
John Best, chief technologist at Hitachi Global Storage Technologies, says perpendicular recording allows two to three times the density of the traditional longitudinal approach. Building on that with other innovations, he expects disk makers will be able to increase capacity further. “Without perpendicular we’d stall and go flat,” he says. “With perpendicular we can keep it moving forward.”
Major disk manufacturers Hitachi Ltd., Toshiba Corp. and Seagate Technology LLC are all working on perpendicular recording. The first commercial products will appear around the end of this year.
Perpendicular recording requires a thicker and differently structured layer of magnetic material on the surface of the disk, but the manufacturing process is essentially the same, Best says.
The technology will be used in microdrives for pocket-sized devices such as smart phones and PDAs, and also in larger systems. Seagate spokesman Michael Hall says increased use of notebooks as desktop replacements is driving demand for more storage in the same space.
And why is perpendicular recording both new and old? Well, it was first demonstrated more than 100 years ago. A Danish scientist named Vladimir Poulsen made the first magnetic recordings of sound in the late 19th century, using a device called a wire recorder. The magnetization in that device was aligned perpendicular to the wire, so in fact perpendicular recording came before the longitudinal type.

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