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Perpendicular Magnetic Recording (PMR)
WD Addresses Hard Drive Capacity Challenge
with PMR Technology
The Perpendicular Recording Solution
F or decades, the hard drive industry has focused almost
exclusively on a method called longitudinal magnetic
recording to record data on hard drives. In longitudinal
In longitudinal recording, as the bits become smaller and closer
together, they experience an increasing demagnetizing field,
recording, the magnetization of each data bit (i.e., the binary much like two bar magnets that are placed end-to-end repel one
digit 0 or 1) is aligned horizontally, parallel to the disk that spins another. Coercivity must be increased to counteract the
inside the hard drive. demagnetization to keep the bits stable under thermal
In perpendicular magnetic recording (PMR), the magnetization fluctuations; otherwise data corruption may occur over time.
of each data bit is aligned vertically to the spinning disk, Higher media coercivity has pushed the recording head write
providing the ability to store more data on a given disk than is field to the limit of known materials.
possible with conventional longitudinal recording. PMR thus In perpendicular recording, the adjacent bits attract instead of
provides a platform for future expansion of hard drive densities. repel (as with bar magnets placed side by side,) creating more
WD will implement PMR technology in calendar year 2006. thermally stable bits. In addition, the media contains a
magnetically soft underlayer (SUL) beneath the recording layer.
The Storage Capacity Challenge
This SUL allows a larger effective write field, thus higher
Since IBM introduced the first hard drive in 1956, the industry coercivity media, enabling further increases in density. Lastly,
has increased storage capacity exponentially to meet an because of the vertical orientation of the bits, the PMR
ever-growing need. Today, the use of consumer electronic recording layer tends to be thicker than that used for
devices that store music, photos, and video, as well as advanced longitudinal recording, providing increased signal for the read
applications including digital video, personal video recorders , heads. All of these benefits enable WD engineers to reliably pack
set-top boxes, network attached storage, and RAID solutions, more data on a given disk than is possible with conventional
are driving the need to pack more and more storage capacity on longitudinal recording
hard drives of all sizes.
The Future
Historically, manufacturers have decreased the size of the
magnetic grains that comprise data bits to increase storage WD will continue to invest in PMR, and other next-generation
capacity on hard drives. Through the years, the development of technologies such as tunneling magneto resistive (TuMR) heads
smaller and smaller data bits has led to higher areal density, or combined with proven ramp load technology. TuMR is a head
number of bits of data that can be recorded onto the surface of a design that provides greater signal output which translates into
hard drive disk. greater signal to noise ratio, enabling higher storage densities.
Ramp load parks the recording head when the drive is idle and
The problem with using this method is that we are rapidly on spin up, maximizing available disk space and minimizing
approaching the point where the microscopic magnetic grains power usage, which results in lower heat and long-term drive
on the disk are so tiny that they could start to interfere with reliability.
one another, thus losing their ability to hold their magnetic
orientations. The resulting data corruption could render a hard WD is committed to the transition to next-generation
drive unreliable and thus unusable. This phenomenon is known technologies while maintaining high standards of quality and
as the superparamagnetic effect (SPE). Improved coercivity, or reliability, as well as the commercial viability of WD products.
the ability of a bit to retain its magnetic charge, is needed to PMR, TuMR, and ramp load will be key technologies during the
overcome SPE. next few years for the hard drive industry to address increasing
demand for high capacity, reliable storage in existing and new
applications. WD's technology implementation strategy is based
on meeting customer needs as we address the hard drive
industry's highest volume markets.
Read/Write Head Read/Write Head
Disk surface
Recording Layer
Soft Magnetic Underlayer
Longitudinal Recording Perpendicular Recording
Longitudinal vs. Perpendicular Recording
Western Digital and WD are registered trademarks; and the WD logo is a trademark Western Digital For service and literature:
of Western Digital Technologies, Inc. Other marks may be mentioned herein that 20511 Lake Forest Drive support.wdc.com
belong to other companies. Product specifications subject to change without notice. Lake Forest, California 92630 U.S.A. www.westerndigital.com
800.ASK.4WDC North America
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