Disk Read/Write Head Technology

The role of the read/write head is to act as a transducer, converting electrical signals to magnetic signals when writing data and the opposite during the read cycle. The read/write heads contain tiny electromagnets which convert the zeros and ones comprising the data bits to and from the magnetic flux reversals which are used to store the data on the platters of the hard disk drive.

The read/write heads role in the correct operation of a hard disk drive is often underestimated, despite them being the most complex component used in a drive. Should the drive suffer a head crash or another failure occur with the read/write heads, you should contact a professional data recovery company, who can recover the data. When a drive suffers a read/write head failure, especially if they have come into contact with the disk platters, can be a complex and lengthy process. If the heads crash into the surface of the platter, they can cause serious damage to the magnetic recording layer which stores the data.

Types of Read/Write Head

The earliest read/write heads, such as ferrite, metal-in-gap (MIG) and thin film, rely upon the two fundamental principles of electromagnetics. Firstly, when electrical current flows through a coil, it produces a magnetic field, which can be used to write data to the magnetic recording layer. Secondly, when a magnetic field comes into close proximity with a coil, an electrical current will flow, which is used to read data from the disk platters.

However, Magnetoresistance (MR) and giant magnetoresistance (GMR) heads use the principle of magnetoresistance. This states that the resistance of a material changes when it is subjected to different magnetic fields. This allows a much higher recording density increasing the maximum capacity of hard disk drives compare to those using electromagnetic heads. These types of heads also use a pair of separate heads, each of which is optimised for its purpose. This contrasts with the conventional read/write heads which used a single head, which was a compromise, allowing the recording density to be further increased.

The use of Tunnelling Magnetoresistance (TMR) heads allowed a further increase in areal density. Such head use microscopic heating coils which control the shape of the transducer region of the head. Soon after, Perpendicular Magnetic Recording (PMR) heads were introduced in which the magnetic field is recorded perpendicular to the surface of the platter. Until this, data was laid down horizontally on the surface, but this type of head allows a huge increase in the areal density, allowing disk drive capacities of over a terabyte to be produced.

Read/Write Heads Bearings

The height of the read/write heads as they fly across the disk surface, known as the “flying height” is critical. It is important that the “flying height” is constant, so that it ensures they will not impact with the platters, resulting in a head crash. To achieve this, air bearings are used, in which air is drawn through the head as the result of the spinning platters, causing a pressure zone below the read/write heads, creating a cushion of air, upon which they float or fly.

The “flying height” has significantly decreased, allowing further increases in recording density. Despite this, improved manufacturing techniques mean the read/write heads are much less likely to crash to impact the disk platters. Head crashes are usually the result of an external impact, such as as dropping an external disk drive or laptop.

Read/Write Head Damage and Data Recovery

When the read/write heads have failed a complete rebuild of the drive by experienced hardware engineers at a professional data recovery company, such as DiskEng, is essential. Any head crash is likely to result in serious damage to the platters which will be seen as unreadable bad sectors when those areas of the disk are accessed. It is important that these areas are avoided as much as possible during the data recovery process, as repeatedly attempting to access damaged areas of the platters can damaged the replacement read/write heads. Such a failure would be likely to cause even further damage to the platters. Our engineers concentrate initially on maximising the yield of good sectors, before attempting to recover sectors from damaged areas of the platters.

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