Have you
heard of the “superparamagnetic effect?” This is a complicated
phenomenon that (theoretically) limits how large typical hard drives can get
and still remain affordable (i.e., going too much beyond 120 Gb/sq. in. or so).
In short, this effect is the result of the use of very fine particles that, when
small enough, begin to lose their ability to hold their magnetic orientation at
room temperature, resulting in flipped
bits. Flipped bits = lost data = useless storage.

Therefore,
scientists and engineers working on magnetic storage had to come up with a
solution. At least for now, there is no way around the superparamagnetic
effect. So, hard drive engineers studied the way that current drives are
constructed. Drives use a technique known as longitudinal
recording to store data. By way of illustration, pretend that you have
a hard drive platter and a whole lot of tiny dominos, each representing a bit
of information. Under the longitudinal recording method, each of these dominos
is laid flat next to one another with their north and south poles (each end of
the domino) pointing parallel to the disk platter. As the bits get pushed closer
and closer together, the risk of corruption as a result of the
superparamagnetic effect increases.

The solution:
perpendicular recording.

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The long and short of recording data

Whereas with
today’s drives, the bits are laid flat, with perpendicular recording, they
stand on end, meaning that more bits can fit into the same space—temporarily
staving off problems related to the superparamagnetic effect. Now, you can have
more bits in the same space and not have to move them closer to one another. (The
space between the bits is called the transition region.)

As you might
expect, the drive mechanics used under perpendicular recording differ from
those used to record longitudinally. The write head for a perpendicularly
recorded drive is much finer, as it has a smaller surface area to work with,
but surprisingly, perpendicular drives could prove to be more tolerant than
their longitudinal counterparts.

Under a
longitudinal recording method, the north and south poles of each bit work
against relatively close bits as a result of magnetic attraction and repulsion.
Since, under perpendicular recording, bits are lined up next to one another
with their poles facing up and down, this magnetic interference is no longer
problematic, resulting in a lessening of randomly flipped bits.

Another
difference between the old and the new is the addition of a thin, soft underlayer
directly beneath the bits. This new platter layer helps the new drive heads
reliably read from and write to the disk. In short, this new layer helps keep a
magnetic field always positive or negative and avoid ambiguity, which would
result in an unusable disk system.

What does
perpendicular recording mean for you? How does 10 times the capacity of today’s
drives for relatively little additional cost sound? Perpendicular recording, as
a result of reorienting the bits (plus some other advances) is expected to
allow drives of up to 10 times the current capacities. Eventually, though, even
these new disks will fall to the superparamagnetic effect, but researchers are
already hard at work on developing a new breed of disks.

Perpendicular
disks are already on the market, too. If you didn’t know it, that indicates how
well these drives are designed. Since only the recording method changed, they
work with existing interfaces, meaning that you can probably pop one in your
system today. For example, you can buy the Seagate Momentus
5400 drive with either a parallel or serial ATA interface.

For those of
you who are children of the ’80s, you probably remember the Saturday morning
educational program, “How a Bill Becomes Law,” which used a
cartoon-like approach to explain the complicated legislative process. Hitachi
has produced something similar that explains perpendicular recording. You need Flash
to view the three-minute long movie: http://www.hitachigst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html.