10 February 2011
Read/write heads are very small parts of the disk drive which move on top of the disk platter and transform the platter’s magnetic field into electrical current and electrical current back into magnetic signals. In essence, then, read/write heads are minute electromagnets which perform conversion from magnetic to electrical information and back.
The distance between the head and the platter is imperceptible to the human eye as it is measured in the millionths of an inch.
The ferrite, metal-in-gap and thin film hard disk heads are the older, conventional hard disk heads. They operate based on the two main principles of electromagnetic force. The first principle is used in writing to the disk and this is that applying an electrical current through the coil will produce a magnetic field. The second principle of electromagnetic force is used when reading back the written information and works opposite to the first—applying a magnetic field to the coil will create an electrical current.
The newer kinds of read/write heads are different in that they do not read the induced current in the coil to read back the information. Instead, they function based on the principle of magnetoresistance, whereby certain materials change their resistance when subjected to different magnetic fields.
These newer MR and GMR heads are also called “dual heads” or “merged heads” because they have separate heads for writing and reading, with each head specializing on a particular function.
The bit size of hard disks is shrinking dramatically through the years and this means that a very great amount of bits are packed into the disks. This necessitates that the magnetic fields should be made very weak so that they do not interfere with one another. This also means that the read/write heads should be correspondingly small and ultra-sensitive to read the weak signals. The new MR and GMR heads are just that—they are so tiny and so sensitive.
Modern drive heads float over the surface of the heads and do not physically touch the platter. The older ones made contact and thus were subject to wear and tear. The space between the head and the platter is called the flying height or floating height or the head gap. This distance is imperceptible to the human eye as it is measured in the millionths of an inch.
Maintaining a certain floating height is essential to precise operation. If the distance is too great, the head cannot read properly and if it is too close to the platter, there is the possibility of a head crash. A head crash can result in data loss, damage to the head, damage to the platter or all of these three. This may be due to contamination stuck in the minute gap between the head and the platter, or a shock applied to the disk while it is in operation.
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