H
ard drive designers have relied on longitu-
dinal recording techniques for more than
half a century, and it has served them well. But
the technology is fi nally nearing the end of its
useful life and will soon be superseded.
With longitudinal recording, 100 or so
microscopic-size magnetically charged grains
comprise a single bit of data. These bits lay
fl at on their backs, oriented end-to-end in
concentric rings around the hard drive’s plat-
ters. Each advance in drive capacity using this
technique has been accomplished by increas-
ing the platters’ areal density—the number of
bits per square inch of disk surface.
But there is a limit to how tightly those
bits can be packed, and when that limit is
exceeded, bits lose their ability to maintain
their magnetic polarity. When the magnetic
grains within a bit spontaneously “fl ip” their
polarity, the data they represent becomes
hopelessly corrupted. The phenomenon is
known as the superparamagnetic effect, and
it’s like Kryptonite to hard drives.
The hard drive industry has long been
aware of the superparamagnetic effect, and
engineers knew it would eventually limit their
ability to increase hard drive capacities. Back
in the 1950s, scientists predicted the effect
would raise its ugly head when areal den-
sity reached 25 megabits per square inch.
Fortunately, those early prognostications
proved to be way off base; in fact, manufac-turers have been so successful at pushing
the barrier that modern drives have achieved
areal density of 110 gigabits per square inch.
This time, however, the experts are really, really
serious about the impending wall.THE INEVITABILITY
OF FAILURE
The superparamagnetic effect can be delayed,
but it can never be defeated. The current
consensus is that the phenomenon will begin
encroaching on drive development by 2006,
when drives reach areal density of 120 giga-
bits per square inch. Faced with this looming
obstacle to progress, engineers have come up
with an alternative to longitudinal recording,
one that promises to dramatically postpone
the superparamagnetic effect. It’s called per-
pendicular recording.
The idea sounds deceptively simple:
Instead of laying the oblong bits fl at on the
disk surface, perpendicular recording stands
them on end so that their positive/negative
polarity is oriented vertically, instead of hori-
zontally. In this scenario, each bit consumesconsiderably less surface area on the platter,
enabling drive manufacturers to pack in dra-
matically more bits. The shift to perpendicular
recording promises an exponential increase
in areal density, a benefi t that will be realized
over the next fi ve to seven years.
When bits are tightly packed in a longitudi-
nal-recording drive, adjacent bits with the same
magnetic polarity—north pole next to north
pole, for instance—tend to repel one another.
The tighter the bits are packed, the more sus-
ceptible they become to fl ipping. The bits in
perpendicular recording are more magnetically
stable because they’re arranged so that one
of the adjacent bits always has the opposite
magnetic polarity—north pole to south pole.
What’s more, the recording media on perpen-
dicular-recording drives is deposited on a soft
magnetic underlayer, which produces a higher
magnetic fi eld that further strengthens each
bit’s ability to maintain its magnetic polarity.NOW THAT’S DENSE
How far will perpendicular recording take us?
According to the most optimistic estimates,r&dBREAKING DOWN TECH —PRESENT AND FUTURE
72 MA XIMUMPC DECEMBER 2005
White Paper: Perpendicular Recording
Technology
Hard drive capacity using
current tech is destined to hit
a wall in less than two years.
Learn how perpendicular
recording technology will
allow manufacturers to blast
right through that barrier
BY JOSH NOREMHOW IT WORKS Perpendicular recording technology explained
LONGITUDINAL RECORDINGRecording
layerRecording
layer
Magnetic
underlayerÑHow magnetic storage works: An electrical current (represented here by the red lines) discharged from the read/write
head passes into the recording layer, magnetizing the particles. The current then returns to the read/write head to
complete the loop. In perpendicular recording, the current passes all the way through the layer and into the magnetic
underlayer before returning to the read/write element.ÑIn longitudinal recording (top), the magnetic bits that represent data are aligned horizontal to the recording media. In
perpendicular recording (bottom), the bits are aligned vertically, so that each bit consumes signifi cantly less space on
the platter, dramatically increasing areal density.Read/write
elementRead/write
elementPERPEDICULAR RECORDING