【 Weak current College 】 hard disk head number

Hard disk head is hard to read the data of the key components, it's main role is to be stored on the hard drive platter of magnetic information into electrical signal transmission to the outside, but it works is the use of special materials for resistance increases as the principle of magnetic field changes to read and write data on the disc, the head of the quality to a great extent determines the hard disc storage density. Currently more popular is the GMR (GiantMagnetoResisive) GMR heads, GMR heads use the magnetoresistance effect better materials and multi-layer film structures, this traditional head than before and MR (MagnetoResisive) reluctance tape heads more sensitive, relative changes can cause of magnetic field to big resistance value changes, thus achieving higher storage density.

The head is in the hard disk platters read write work tool, hard drive one of the most sophisticated of sites. The head is used in core coil winding up. Hard drive as you work, head through the induction rotating platter magnetic field changes to read the data; by changing the platter of magnetic field on which to write the data. To avoid Magnetic heads and disc wear, working state, the head of the high speed rotating platters, but not in direct contact with the disc, and only after the power is off, the head will automatically return to the disc at a fixed location (known as the landing area, where disc does not store data, is the starting position of the disc).

As the head of the nature of the work on its magnetic sensitivity and precision requirements are very high. Previous head adopts magnetic material, magnetic susceptibility, is not very satisfactory, and therefore early hard drive single disc capacity is relatively low, single disc capacity is big then the disc on the track density, magnetic induction enough, there is no way to accurately read the data. This results in earlier drive capacity is very limited. As technology evolves, head in the magnetic susceptibility and precision has made great strides.

The original head is reading and writing function together, the head of the manufacturing process, the technology requires very high, and for the PC, to Exchange data with the hard disk, read data far faster than writing, reading and writing operations both properties are also completely different, and this led to read, write, separation of the head, the not respectively work.

Thin-film magnetic induction (TEI)
Between 1990 and 1995, the hard drive using TFI read/write technology. TFI head is actually wound cores of. Disc in winding through the cores in the head on the induction voltage. TFI read heads can reach its capacity limit, because of the sensitivity of the magnet, but it's writing has weakened.

Anisotropic magneto resistance (AMR) head
AMR (AnisotropicMagnetoResistive) in the mid-1990s, Seagate company launched use AMR head of the hard disk. AMR heads use complete TFI head to write operation, but with a thin strip of magnetic materials as the reading component. In a magnetic field exists, the thin strip of resistance will change with the magnetic field, which in turn produces a very strong signal. Hard drive decipher due to magnetic field polarity change due to changes in thin section resistance, improves reading sensitivity. AMR head further increased areal density and reduces the number of components. Because the AMR changes the amount of resistance have a certain limit, the AMR technology can support 3.3GB/square inch of recording density, AMR head of sensitivity limit also exist. This causes the GMR heads of research and development.

GMR (giant magneto resistance GiantMagnetoResistive,)
GMR head has inherited the TFI head and AMR head with read/write technology. But it's read heads for the magnetic variation on the disks show a higher sensitivity. GMR head is made of 4 layers of conductive materials and magnetic thin films formed: a sensor layer, a non-conductive intermediate layer, a magnetic Plug and an Exchange layer. GMR sensor sensitivity than AMR head big 3 times, so to increase the disc's density and performance.

Hard disk number of the head depends on the number of discs in the hard disk, both disks are stored at the data, so a disc map two heads to work properly. For example, the total capacity of the hard disk, using 80GB single disc capacity of the disc, 80GB that only one disc, disk slices back have data, the corresponding two heads; and similarly 120GB hard drive capacity, uses two platters, only three heads, one disc side without head.