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How can a 3.5-inch standard hard
disk drive (HDD)
possibly hold a terabyte
of information? As manufacturers reached the limits
of hard
drive capacity, consumer demand for even
higher capacity drives did not diminish. A
relatively new recording technology called
perpendicular recording, is being deployed to
further increase hard
drive storage capacities.
To understand how perpendicular
recording has changed hard
disk storage and increased storage
capacities, you first need to understand
conventional, longitudinal
recording.
Longitudinal
Recording
As indicated by the name, longitudinal
recording is a method of recording data
to a hard
disk drive (HDD)
in such a way that the data
bits
are aligned horizontally in relation to the drive's
spinning platter,
which is parallel to the surface of the disk.
Essentially, you are recording on a magnetic
material, where bits
(a collection of magnetized particles) are laid out
end-to-end. Longitudinal
recording is the actual method of how the
bits
are recorded on disk platters.
The direction of this magnetic charge is horizontal
to the media, meaning the north and south poles of
the magnetized particles are lined parallel to the
surface of the disk.
Longitudinal
recording has been the standard method of
recording for more than 50 years — the first
commercial hard
drive was introduced in 1956. Over the
years we have seen many technological changes to longitudinal
recording, which have resulted in
higher-capacity drives. We've moved from 5.25 inch
drives to 2.5 inch drives, the number of platters
and heads have been reduced all the while increasing
aerial density (which is the amount of data
per square inch of media). With all of these changes
however, the need to physically change the way data
was written to the drive was also being considered
to reach higher storage capacities.
Storage capacity with longitudinal
recording was largely increased by
decreasing the size of the magnetic grains that
make-up data
bits.
As the magnetic grains became smaller, more data
could then be stored on the disk. Unfortunately,
magnetic grains have their limits. By continuing to
shrink them, the point where data
integrity would be compromised was on the horizon.
This effect is called the superparamagnetic
effect.
The Superparamagnetic
Effect
In magnetic disk drive storage technology, the superparamagnetic
effect refers to the fluctuation of
magnetization due to thermal agitation. When the
aerial density (the number of bits
that can be stored on a square inch of disk media)
of a disk medium reaches 150 gigabits
per square inch, the magnetic energy holding the bits
in place on the medium becomes equal to the ambient
thermal energy within the disk drive itself. When
this happens, the bits
are no longer held in a reliable state and can
"flip," and scramble the data
that was previously recorded.
Because of superparamagnetism,
hard
drive technologies were expected to stop
growing once they reached densities of 150 gigabits
per square inch. Of course, when you see a hard
drive manufacturer announce a 400GB
hard
drive you may wonder what happened to the
superparamagnetic
effect? Actually, this type of drive
would contain three platters
able to store up to a maximum of 133GB
each resulting in a 400GB
HDD,
it is not 400GB
contained on a single platter.
Perpendicular
Recording
Realizing the limits of packing smaller magnetic
grains was heading towards occurrences of superparamagnetism,
manufacturers still needed a way to pack more data
onto each drive. Perpendicular
recording differs from longitudinal
recording in that data
bits
are aligned vertically (not horizontally) — or
perpendicular to the disk, which allows for
additional room on a disk to pack more data,
thus, enabling higher recording densities. It is
widely believed that with perpendicular
recording, the superparamagnetism
barrier can be pushed further back allowing for
continued growth in the aerial density of the media
for some time.
Hitachi® believes
this recording technology, in time, can result in a
3.5-inch disk drive capable of storing an entire terabyte
of data.
Not only will perpendicular
recording have an effect on desktop
storage, but on consumer devices as well, which is a
major driving force in storage sales. Smaller drives
(1.8 inch), like those used in the popular Apple®
iPod® will also grow in capacity. In
due time we will see the iPod® and
similar devices offer 80GB
of storage and higher. Alternatively, it could be
used to produce much thinner and slimmer high
capacity hard
drives for consumer devices. Where you
can store 3,000 on some of the higher-end MP3
players today; image being able to store 30,000
songs on one.
Perpendicular
recording technology, however, will not
start and stop with changing the way data
bits
are aligned. Much like the growth in capacity with longitudinal
recording, technological advancements in platters;
read/write
heads,
and physical disk media surfaces to name a couple,
will contribute to advancements in the capacity
growth of perpendicular hard
disk drives.
Perpendicular
recording technology also is not the
answer to removing superparamagnetism.
It has not stopped the search for the ever elusive
answer to being able to further shrink the actual
size of the magnetic grains that make up data
bits.
Perpendicular
recording only moves the superparamagnetism
barrier back a bit,
it doesn't eliminate it. For now Perpendicular
recording technology allows for many new
developments and advancements in storage capacity
over the coming years, but it too will feel
eventually feel the pull of the superparamagnetic
effect; unless the physical size of a bit
can be further reduced, then again that barrier will
be pushed back to meet the ever-growing storage
needs of consumers.
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