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Magneto-Resistive Heads
Seagate Technology
920 Disc Drive
Scotts Valley, CA 95066-4544
408-438-6550
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The data storage industry is on a perpetual quest to place the maximum amount of storage in the smallest size possible, and MR heads will become one of the important means to achieving new capacity and performance milestones towards this goal. Magneto-resistive (MR) heads allow drive manufacturers to increase the capacity of drives without sacrificing performance or significantly increasing costs. MR heads have unique properties which make them especially useful for small form-factor drives, but can also be applied to achieve higher performance and greater capacity in larger disc drives.
The Magneto-Resistive Effect
Most disc drives built today use inductive thin-film recording heads. In essence, these heads are similar to the recording head on an audio cassette player, where the read element of the head detects changes in the magnetic flux on the surface of the recording media. When an inductive thin-film head passes over a magnetic field, ft generates a minute signal which is subsequently amplified, filtered and converted into its digital representation by the electronics on the disc drive's circuit board.
MR heads operate on a completely different physical phenomenon known as the magnetoresistive effect. Certain metals, when exposed to a magnetic field, change their resistance to the flow of electricity. This property is exploited in creating the read element of an MR head. Reading information for the media is accomplished by constantly passing a sense current through the read element of the head. When the head passes over a magnetic field on the media, the head changes its resistance, which is detected by the change in amperage of the sense current.
Increased Recording Densities
A big advantage of MR heads is that they enable disc drives to reach much higher capacities than the mainstream, high-volume disc drives on the market today. This is because MR heads can read signals better than inductive thin-film heads when bits are packed ever more closely together. They are also able to better distinguish bits between adjacent tracks as those tracks are brought closer together. Disc drive designers can, as a consequence, build drives with higher areal densities than ever before. Seagate Technology has developed its second-generation of thin-film (MR) heads, which enables a 30% increase in track density, and about 15% higher bit density over drives in the market today.
Other Improvements
Many of the problems facing design engineers today revolve around the limitations and idiosyncrasies of conventional inductive thin-film recording heads. First, inductive thin-film heads have the troublesome side effect of creating tiny valleys, or undershoots, on either side of the signal peaks. This phenomenon is intrinsic to the operation of all conventional thin-film heads; and creates more work for the drive, since additional circuitry is required to filter out the unnecessary valleys. In contrast, MR heads produce a well-formed signal crest with no undershoot, simplifying both the design and implementation of the drive.
Conventional thin-film heads are also dependent on the rotational speed of the recording media. Specifically, their proper operation relies on the disc rotating within a required linear velocity. This
becomes a significant limitation with smaller form factor designs. AS the disc diameter shrinks, the linear velocity decreases, even though the spindle speed remains constant. Conventional thin-film heads, in effect, can't handle the slower linear track speed. MR heads, however, are not speed-dependent, and can operate at a spectrum of spindle speeds. This will become more significant as higher-capacity drives emerge in 2.5-inch and smaller form-factors. MR heads are, in fact, ideally suited for use in small form-factor drives, since they simultaneously provide higher areal densities and are insensitive to linear velocity.
Perfecting the Technology
The advent of MR heads does not signal the imminent demise of the conventional thin-film head. In fact, such heads still have significant potential for increased areal densities in low-cost disc drives. MR heads, however, represent one of the cutting-edge technologies of magnetic data storage and will be needed soon enough to reach capacities for desktop computers to reach multiple Gigabytes on a single-platter drive. Seagate has been developing this technology for more than ten years, and by becoming an early developer of the technology, Seagate is positioned to meet demand for the capacities MR heads enable.
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