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AMR and GMR Heads Increase Hard Drive
Capacity in Western Digital Drives
Anisotropic Magnetoresistive and Giant Magnetoresistive
Head Technology Taking Over Hard Drives

OVERVIEW/EXECUTIVE SUMMARY
Error rate, the number of data bits correctly decoded by the recording head and fly height,
the distance between the read/write elements of the head and the magnetic layer of the
media are key design parameters in the quest for higher areal density.

Designers strive to keep error rate and fly height as large as possible. Error rate for
performance reasons and fly height for reliability. For a given head technology, however,
these are mutually exclusive goals. To achieve higher areal densities with thin film inductive
(TFI) heads, fly heights had to decrease in order to maintain acceptable error rates.
Increasing the ability of the head to detect magnetic signals (i.e. head sensitivity) and slow
the rate at which fly height decreased was possible for a time. Eventually, new technologies
were needed. Hence the development and introduction of Magneto-Resistive (MR), both
anisotropic and giant magnetoresistive, technology. See Figure 1 for a comparison of
anisotropic MR and giant MR technologies.

Anisotropic Magnetoresistive (AMR) head technology is currently the primary read/write
head technology used in hard drives, replacing TFI heads, the previous standard in the
marketplace. GMR heads will be the dominant head technology by the end of 1999.
Western Digital is incorporating AMR heads from IBM, Read-Rite and others as well as
GMR heads from IBM in desktop drives today. GMR heads from other suppliers will be
making their way into drives in the second half of 1999.
AMR vs GMR Error Rate / Yield Comparison

4.0

3.5
% Error Rate > 1E-5

3.0 AMR
2.5

2.0

1.5
GMR Wr = 0.95