The heads are the read/write interface to the magnetic physical media on which the data is stored in a hard disk. The heads do the work of converting bits to magnetic pulses and storing them on the platters, and then reversing the process when the data needs to be read back. Heads are one of the more expensive parts of the hard disk to enable areal densities and disk spin speeds to increase.
However GMR heads is most popular in the today’s hard disk, there have several technologies been proposed at several times for read/write heads:
- Ferrite Heads
- Metal-In-Gap (MIG) Heads
- Thin Film (TF) Heads
- Anisotropic Magneto resistive (AMR/MR) Heads
- Giant Magneto resistive (GMR) Heads
- Colossal Magneto resistive (CMR) Heads
Read/write heads are an extremely critical component in determining the overall performance of the hard disk, since they play such an important role in the storage and retrieval of data. New head technologies are often the triggering point to increasing the speed and size of modern hard disks therefore read/write heads are the most sophisticated part of the hard disk, which is itself a technological marvel.
Each bit of data to be stored is recorded onto the hard disk using a special encoding method that translates zeros and ones into patterns of magnetic flux reversals. Each hard disk platter has two surfaces used to store the data generally and there is normally one head for each surface used on the drive. Since most hard disks have one to four platters, most hard disks have between two and eight heads. Some larger drives can have 20 heads or more. Only one head can read from or write to the hard disk at a given time. Special circuitry is used to control which head is active at any given time.
The head floats over the surface of the disk and do all of their work without ever physically touching the platters. The amount of space between the heads and the platters is called the floating height or flying height or head gap. The read/write head assemblies are spring-loaded using the spring steel of the head arms which causes the sliders to press against the platters when the disk is stationary.
This is done to ensure that the heads don't drift away from the platters therefore maintaining an exact floating height is essential for correct operation. When the disk spins up to operating speed, the high speed causes air to flow under the sliders and lift them off the surface of the disk. The distance from the platters to the heads is a specific design parameter that is tightly controlled by the manufacturers.