Number of heads

Introduction to the number of heads

The number of heads (Heads). The function of the heads is to convert magnetoelectricity. The cost of the heads accounts for about 40% of the total cost of the hard disk. Breakthrough, then the technology of the magnetic head must be developed. Under normal circumstances, a disc has only one head, but with the latest technology, two heads can read one disc at the same time.

In the LBA mode, the maximum number of heads that can be set is 255

Introduction to the head

The hard disk head is the key component of the hard disk to read data, and its main The function is to convert the magnetic information stored on the hard disk disk into electrical signals for external transmission, and its working principle is to use the principle that the resistance value of special materials will change with the magnetic field to read and write data on the disk. The magnetic head is good. Badness largely determines the storage density of hard disk platters. GMR (Giant Magneto Resisive) giant magnetoresistive heads are currently more commonly used. GMR heads use materials with better magnetoresistance effects and a multilayer film structure, which is more than traditional heads and MR (Magneto Resisive) magnetoresistive heads. To be sensitive, relative magnetic field changes can cause large resistance changes, thereby achieving higher storage density.

The magnetic head is a tool for reading and writing the disc in the hard disk, and it is one of the most precise parts of the hard disk. The magnetic head is made by winding a coil on a magnetic core. When the hard disk is working, the magnetic head reads data by sensing the change of the magnetic field on the rotating disk; and writes data by changing the magnetic field on the disk. In order to avoid the abrasion of the magnetic head and the disc, in the working state, the magnetic head is suspended above the high-speed rotating disc without direct contact with the disc. Only after the power is turned off, the magnetic head will automatically return to the fixed position on the disc ( Called the landing zone, where the disc does not store data, it is the starting position of the disc).

Due to the working nature of the magnetic head, the requirements for its magnetic induction sensitivity and precision are very high. Earlier magnetic heads used ferromagnetic materials, which were not very ideal in terms of magnetic induction sensitivity. Therefore, the capacity of single disks of early hard disks was relatively low. If the capacity of a single disk is large, the track density on the disk will be large, and the magnetic head will not be able to read accurately due to insufficient magnetic head induction. Data. This caused the early hard disk capacity to be very limited. With the development of technology, magnetic heads have made great strides in magnetic induction sensitivity and precision.

In the beginning, the magnetic head has read and write functions together. This requires high manufacturing process and technology of the magnetic head. For personal computers, in the process of exchanging data with the hard disk, reading data is far away. Much faster than writing data, the characteristics of the read and write operations are also completely different, which leads to separate read and write heads, which work separately and do not interfere with each other.

Thin film induction (TFI) head

From 1990 to 1995, hard disks used TFI read/write technology. The TFI head is actually a wire-wound magnetic core. When the disk passes under the wound core, an induced voltage is generated on the magnetic head. The reason why the TFI read head reaches the limit of its capability is that its write capability is weakened while increasing its magnetic sensitivity.

Anisotropic Magneto Resistance (AMR) heads

AMR (Anisotropic Magneto Resistive) In the mid-1990s, Seagate introduced hard drives using AMR heads. AMR heads use TFI heads to complete the write operation, but use thin strips of magnetic material as the reading element. In the presence of a magnetic field, the resistance of the thin strip will change with the magnetic field, thereby generating a strong signal. The hard disk deciphers the change in the resistance of the thin strip caused by the change in the polarity of the magnetic field, and improves the reading sensitivity. The AMR head further increases the areal density and reduces the number of components. Since the resistance change of the AMR film has a certain limit, the AMR technology can support a maximum recording density of 3.3GB/square inch, so the sensitivity of the AMR head also has a limit. This led to the development of GMR heads.

GMR (Giant Magneto Resistive)

The GMR head inherits the read/write technology used in the TFI head and the AMR head. But its read head shows higher sensitivity to magnetic changes on the disk. The GMR head is composed of 4 layers of conductive and magnetic material films: a sensing layer, a non-conductive interposer, a magnetic plug layer and an exchange layer. The sensitivity of the GMR sensor is three times greater than that of the AMR head, so it can improve the density and performance of the disc.

The number of heads of a hard drive depends on the number of discs in the hard drive. Data is stored on both sides of the disc, so one disc corresponds to two heads to work normally. For example, for a hard disk with a total capacity of 80GB, if a single-disk capacity of 80GB is used, there is only one disk, and the disk has data on the front and back, corresponding to two heads; while the hard disk with the same total capacity of 120GB uses two disks. There are only three heads, one of which has no head on one side.

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