ince the first time "Get Perpendicular" got stuck in our heads, we've anxiously anticipated the arrival of perpendicular recording technology. The wait has been long, especially on the desktop, but perpendicular recording has finally arrived in Seagate's Barracuda 7200.10 hard drive. And it's arrived in style. Seagate has exploited the new recording technology to offer a drive with a monstrous 750 GB capacity—50% more than any other drive on the market. Perpendicular recording does wonders for storage capacity, and thanks to denser platters, it can also improve drive performance. Couple those benefits with support for 300 MB/s Serial ATA transfer rates, Native Command Queuing, and up to 16 MB of cache, and the Barracuda 7200.10 starts to look pretty appealing. Throw in an industry-leading five year warranty and a cost per gigabyte that's competitive with 500 GB drives, and you may quickly find yourself scrambling to justify a need for 750 GB of storage capacity.
Perpendicular recording is believed to be capable of delivering up to 10 times the storage density of longitudinal recording, on the same recording media. There was some interest in using the system in floppy disks in the 1980s, but the system was never reliable. Today there is renewed interest in using it for hard drives, which are rapidly reaching their fundamental limits.
Current hard disk technology with longitudinal recording has an estimated limit of 100 to 200 gigabit per square inch due to the Superparamagnetic effect, though this estimate is constantly changing. Perpendicular recording is predicted to allow information densities of up to around 1 Tbit/sq. inch (1000 Gbit/sq. inch)
The main challenge in designing magnetic information storage media is retaining the magnetization of the medium despite thermal fluctuations. If the thermal energy is too high, there may be enough energy to reverse the magnetization in a region of the medium, destroying the data stored there. Since the energy required to reverse the magnetization of a magnetic region is proportional to the size of the magnetic region (where a larger magnetic region is more stable), there is a minimum size for a magnetic region at a given temperature. If it is any smaller it is likely to be randomly de-magnetized. Perpendicular recording keeps the same region sizes as in standard magnetic media, but organizes the magnetic regions in a more space-efficient way.
The popular explanation for the advantage of perpendicular recording is that it achieves higher storage densities by aligning the poles of the magnetic elements, which represent bits, perpendicularly to the surface of the disk platter, as shown in the illustration. Aligning the bits in this manner takes less platter than what would have been required had they been placed longitudinally. So they can be placed closer together on the platter, thus increasing the number of magnetic elements that can be stored in a given area. The true picture is a bit more complex, having to do with the use of a magnetically "stronger" (higher coercivity) material as the storage medium. This is possible due to the fact that in a perpendicular arrangement the magnetic flux is guided through a magnetically soft (and relatively thick) underlayer underneath the hard magnetic media films (considerably complicating and thickening the total disk structure). This soft underlayer can be effectively considered a part of the write head, making the write head more efficient, thus making it possible to produce a stronger write field gradient with essentially the same head materials as for longitudinal heads, and therefore allowing for the use of the higher coercivity magnetic storage medium. A higher coercivity medium is inherently thermally more stable, as stability is proportional to the product of bit (or magnetic grain) volume times the uniaxial anisotropy constant Ku, which in turn is higher for a material with a higher magnetic coercivity.
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