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Hard Disk Read/Write Head Technology

The read/write head is designed to act as a transducer, which converts electrical signals into magnetic signals during writing and the opposite when reading data. Tiny electromagnets are used in read/write heads to convert the zeros and ones used to signify each bit to and from the magnetic flux reversals stored on the platters of the hard disk drive.

It is easy to overlook the role read/write heads play in the correct operation of hard disk drives, but they are the most sophisticated component in drive. A head crash or other failure of the read/write heads requires professional data recovery services to provide the solution. Data recovery following a read/write head failure, particularly if they’ve impacted with the disk platters, is a complex process. A head crash can cause a lot of damage to the magnetic recording layer.

Read/Write Head Types

The original read/write heads, including ferrite, metal-in-gap (MIG) and thin film, use the two main principles of electromagnetics. The first is that when electrical current flows through a coil a magnetic field is produced, which is used when writing data to the disk platter. The second is that when a magnetic field is in close proximity to a coil it will induce an electrical current to flow, used when reading data from the disk platter.

Rather than using the induced current in the coil, Magnetoresistance (MR) and giant magnetoresistance (GMR) heads rely on the principle of magnetoresistance, whereby the resistance of the material changes when subject to different magnetic fields. Considerably higher recording density was possible allowing the maximum capacity of hard disk drives to be increased. By using two separate heads each can be optimised for their purpose, in contrast to conventional read/write heads where a compromise was required; allowed a further increase in recording density.

A further increase in hard disk capacity was made possible by Tunnelling Magnetoresistance (TMR) which uses microscopic heating coils to control the shape of the transducer region of the head. Perpendicular magnetic recording (PMR) was introduced soon after where the magnetic field is recorded perpendicular to the surface of the platter, allowing a huge increase magnetic density, making disk capacities in the terabyte range possible.

Air Bearings for Read/Write Heads

An extremely important aspect of read/write heads is that they must fly at a constant “flying height” above the surface of the disk platters. This ensures that they do not impact with the platters, which would result in a head crash. Air bearings are used, where the action of the spinning platters induces air to be drawn through the head, which causes an area of pressure whereby the read/write heads float on a cushion of air.

Although the “flying height” has been significantly decreased with an increasing recording density, the read/write heads are now a lot less likely to crash into the disk surface. The majority of head crash events are the result of an impact, caused by such accidents as dropping an external USB drive or laptop.

Read/Write Head Impact in Data Recovery

Failures of the read/write heads require a complete rebuild of the drive by an experienced hardware engineer at a professional data recovery company, such as DiskEng. In the event of a head crash the platters will suffer damage which will cause errors when reading some areas of the disk. The data recovery process must avoid these areas as much as possible during while securing an image, as the replacement read/write heads may become damaged which could cause further damage of the platter surface to occur.

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