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The Story Of GMR Heads
lopati writes "The story of GMR heads, "the breakthrough that boosted the capacity of hard-drives from a few gigabytes to 100 gigabytes and more--came from chance observation, basic research and a vast, painstaking search for the right materials." Check out the helpful infographic." Background: This is a story, essentially, about how hard drives broke through some of the space limitations at the beginning of the 1990s - pretty cool background.
IBM's major problem was that, although they were able to scale down the GMR head very easily, they had large stocks of old media that was not certified for use on GMR drives. (Incidentally, most of that media is in an enormous warehouse in Hungary, which is where most of their drives are produced now.) They designed a recertification process that was supposed to allow them to separate the media that would be suitable for the 75GXPs from the media that wasn't suitable, but that process was deeply flawed and this resulted in the high failure rates of their drives.
You may find it a bit odd to be hearing this from a former Maxtor employee. Well, the dirty little secret of storage companies is that reverse engineering is rampant. My colleagues at Maxtor probed, disassembled, and tested the IBM drives; indeed, they might have known what the bug was even before IBM did.
So, the obvious RISK of GMR technology is: do not use platters that are not certified for use with the new heads. Those who disregard this creed are certain to meet with a nasty public relations disaster in due time.
freebsd guy
One of my physics profs, Yumi Ijiri, moved to my school after doing a few years of research for NIST and IBM regarding GMR technology. Basically, noone could figure out why GMR worked, or how to systematically improve upon the concept. IBM found a neat combination of thin films created these extremely sensitive magnetic sectors, and instead of finding out why/how it works, they empirically tried some 22000 or so combinations until they progressively found better and better arrangements. After the fact, they hired Yumi to figure all the physics out, but her research was also inconclusive. It kinda scares me that there's stuff in my harddrive that IBM and NIST couldn't figure out after 4 years of research.
This is where I get my recommended daily allowance of "Foot in Mouth."
You start combining the elements of course. 100x99x98/6 is about 160,000, which is the number of different combinations of 3 elements you can have. But then you can also continually adjust their relative concentrations - A B_x C_y allowing x and y to be any number between 0 and infinity - in practice you might sample at 10 different points in x and y to get a rough idea: that's another factor of 100, so about 10 million ways to combine three elements just in terms of chemistry. Go look at alloy phase diagram books for a sample of the complexity you can get combining three metallic elements into alloys. And why stop at 3 elements? The high T_c superconductors take 4 or 5 or more to work.
:-) And so difficult :-(
But this isn't just chemistry either - the material is nonuniform, layered. Each layer can be composed of some different magnetic or non-magnetic alloy, and each layer can have a different thickness, and the number of layers is itself a variable. The combinatorial possibilities are in the billions! Obviously they narrowed it down considerably to find what they needed in just 30,000 samples - but there may be something even more spectacular out there among the billions of other possibilities, just waiting to be found.
That's what makes science these days so interesting
Energy: time to change the picture.