Giant Magnetoresistive effect
A revolution in the Hard disk drive industry
IBM and the birth of the hard drive
On September 13, 1956, a small team of IBM engineers in San Jose introduced the first computer disk storage system. The 305 RAMAC (Random Access Method of Accounting and Control) could store five million characters (five megabytes) of data on 50 disks, each 24 inches in diameter. RAMAC's revolutionary recording head could go directly to any location on a disk surface without reading all the information in between. This IBM innovation made it possible to use computers for airline reservations, automated banking, medical diagnosis and space flights. Other IBM innovations during this period included:
"Write wide, read narrow" (1957), which made it possible to read data accurately even if tape heads were out of alignment.
and
Multiple density support (1957), which allowed users to read tape written on older machines, preserving the investment which IBM customers had made in the previous generation of magnetic storage.
As computerized information increases and new technologies such as digital video and multimedia hit the mainstream, demand grows for new and better ways of storing digital information. Using a scientific discovery from the 1980s, IBM recently introduced a break-through disk drive technology, including a model with 16.8 gigabytes of disk space-enough to hold eight hours of full-motion video.
How it Works
Giant Magnetoresistive Technology
IBM's disk storage revolution stems from the "giant magnetoresistive" (GMR) effect, discovered in the late 1980s by two European scientists. In essence, the GMR effect demonstrated large resistance changes in a magnetic field for certain materials composed of alternating thin layers of various metallic elements.
IBM scientists saw the potential for what this discovery could do for disk drive technology. Using their own innovations, IBM's research teams developed GMR technology and incorporated it into the recording head of a disk drive. In disk drives data is stored as tiny magnetized regions called bits on a disk. Depending on its orientation, a bit can represent a "1" or a "0." A writing element writes bits onto the disk and a reading element reads them by detecting the presence of their faint but tell-tale magnetic fields. GMR represents a leap in reading element technology.
Spin Valves
A key to using this technology in computer products was finding a way to quickly and efficiently locate and identify these tiny magnetized bits on a disk. The solution, again related to the GMR effect, was "spin valves," where the very small fields from the tiny bits rotates the magnetization direction in an "unpinned" magnetic layer in relation to a the magntization direcrion of a "pinned" magnetic layer. The resulting change in electrical resistance allows the information stored in the bit to be read by electronics in the disk drive.
IBM is making its GMR disk drive technology available for desktop computers in its Deskstar 16GP family of disk drive products. They will range from a 3.2-gigabyte model to the 16.8-gigabyte disk drive.
More media info
Micrograph of one of IBM’s pioneering giant magnetoresistive (GMR) heads, the most sensitive of its kind for writing and reading data on a computer’s magnetic hard disk drive. By passing a pattern of current pulses through the large coil in the center of the image, magnetic fields are induced and concentrated at a tiny gap, located beneath the tip in the lower center. The fields, in turn, write bits onto the hard disk as a concentric pattern of magnetized regions called a data track. To read the bits, the magnetic fields emanating from the disk change the electrical conductivity of an extremely sensitive GMR element, which sits right behind the gap. Electronics in the disk drive detect the conductivity changes and convert them back into a pattern of digital data.
In 1997, IBM was first to introduce the GMR head into products, stimulating hard-disk-drive data densities to increase from 60 percent to 100 percent (doubling) each year.
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IBM's data-density world-record of 35 billion bits per square inch
Pictured are two tracks of magnetic bits written onto a hard disk at IBM's Storage Systems Division in San Jose, Calif. The fainter, top track is recorded at IBM's new world-record density of 35 gigabits per square inch, more than three times denser than today's most sophisticated products. The lower track is recorded for comparison at 23 gigabits per square inch.
IBM announced the new world record Monday (October 4, 1999).
This image is made using a magnetic force microscope, which uses the motion of a tiny magnet-tipped cantilever to detect magnetic fields emanating from a surface. The field of view is 1.85 microns, less than 1/50th the diameter of a human hair.
The lines shown in the second image represent the magnetic field intensity averaged across the tracks, demonstrating how the bits can be clearly detected even when the pattern appears visually to be quite faint.
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Did you ever wonder how your hard disk drive works?
Without it, your computer would feel empty inside
Magnetic hard-disk drives are used to store most of the data accessible by personal computers and workstations, as well as much of the data being processed by large enterprise servers. The data is stored digitally as tiny magnetized regions, called bits, on the disk. A magnetic orientation in one direction on the disk could represent a "1", an orientation in the opposite direction could represent a "0". Data is arranged in sectors along a number of concentric tracks. These tracks are arranged from the inner diameter of the disk to near its outer edge. Disk drives may contain more than one disk in a stacked assembly. Data is written onto each disk surface (top and bottom) by a separate recording head. So a disk drive with three disks will usually have six separate recording heads.
You're not the only one who can read and write
In modern disk drives using the IBM innovations of magnetoresistive (MR) or giant magnetoresistive (GMR) heads, the bits are written and read by separate elements in a recording head as it flies over the spinning disk. A writing element writes bits onto the disk and a reading element read the bits by detecting the presence of their faint but tell-tale magnetic fields. The head itself is attached to a slider, an aerodynamically shaped block that allows the head to maintain a consistent flying height above the disk. In turn, the slider is connected to a suspension arm that is controlled by an actuator which can move the head to any track of bits on the disk, from the inner to the outer diameter. Special electronic circuits encode data from the computer's processor prior to writing, and decode the bit pattern after reading. Additional vital electronic circuits keep track of where data is stored on the disk so that it can be readily retrieved when needed, and monitor the motion of the disks and heads so their positions over the disks is always known precisely.
Keep reading -- this is the juicy part
When a command is made to store some data on a disk, the following chain of events occurs:
- The data flows into a cache where it is encoded using special mathematically derived formulae, ensuring that any subsequent errors caused by noise can be detected and corrected.
- Free sectors on the disk are selected and the actuator moves the heads over those sectors just prior to writing. (The time it takes the actuator to move to the selected data track is called the "seek" time.)
- Once over the data track, the heads must not write the data until the selected free sectors on that track pass beneath the head. This time is related to the rotation speed of the disk: the faster the speed, the shorter this "latency" period.
- When it's time to write, a pattern of electrical pulses representing the data pass through a coil in the writing element of the recording head, producing a related pattern of magnetic fields at a gap in the head nearest the disk. These magnetic fields alter the magnetic orientations of bit regions on the disk itself, so the bits now represent the data.
When a command is made to read some data on a disk, a similar process occurs in reverse. After consulting the table of stored data locations in the drive's electronics, the actuator moves the head over the track where the chosen data is located. When the correct sectors pass beneath the head, the magnetic fields from the bits induce resistivity changes in the sensitive MR or GMR materials located in the reading elements within the head. These elements are connected to electronic circuits, and the current flowing through those circuits change with the resistivity changes. The current variations are then detected and decoded to reveal the data that had been stored on the disk.
Faster, smaller, cheaper, better -- we're up to the challenge
As manufacturers such as IBM improve the capacity and performance of disk drives, each of the elements involved must be improved. To name just a few: magnetic materials on the disk must be made finer so smaller bits can be written and still be read; read elements must be made more sensitive so they can read the smaller bits; smooth operating motors and lubricants must permit the disk to be spun faster to reduce latency; the actuator's electrical and mechanical systems must be improved to position the head accurately over narrower tracks in less time (to reduce the seek time); the disk drive's electronics must be upgraded to manage -- without errors -- the increasing torrent of data flowing in and out of the heads when smaller bits pass by at faster speeds.
Leading the way in storage (Think Research - 1997)
IBM Storage & Storage Systems
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GMR 101: Visualize MR and GMR Heads in action
Advanced GMR: Observe the physics of GMR in motion
IBM Fellow Stuart Parkin with GMR sputtering apparatus