The platters of the hard disk are coated with a thin magnetic layer. They are mounted on the rotating part of the spindle motor. Magnetic heads are moved over the surface of the plates using a voice coil drive. On the magnetic head there is a slider with an integrated microscopic assembly consisting of a reading element capable of converting the transitions of magnetization of the magnetic layer into electrical pulses and a recording element that converts pulses into transitions of magnetization of the magnetic layer. All data is stored on the platters of the hard disk in the form of transitions between the directions of magnetization, arranged in the form of concentric tracks.

A track is the path that the head travels over the surface of the platter while reading / writing data.

Zones are imaginary rings, into which the platters of the hard disk are divided, each ring has a different recording frequency. The zones are numbered from the outer ring to the inner ring.

The zone allocation table displays the sector density per track (SPT), which is different for each zone.

User data is stored in the work area in data sectors, which are located on data tracks. In the characteristics of the hard disk model, the capacity of this particular area is indicated. It is an unbroken chain of logical sectors (LBA). Each LBA is referenced through a number, starting at 0 and ending with the maximum available sector, called the MAX LBA. These numbers are transmitted in read / write commands by the operating system disk device driver through the interface.

The connection between the linear logical disk space LBA and the arrangement of physical sectors by tracks, heads and zones is carried out through a special program - a translator.

The translator (translation program) maps the logical sector with the LBA number to the physical sector with the coordinates of the track, head, sector, zone, taking into account the zonal distribution of SPT (sectors per track) and defective sectors and tracks excluded from work.

The modern technology of manufacturing magnetic disks does not allow making disks without defects. All bad sectors must be excluded from the LBA number sequence. To store the numbers of defective sectors, the hard disk has a spare space hidden from the user and accessible only to the control program. Bad sector numbers are entered into a table at the factory during the production of a hard disk. This is called defect hiding. This is necessary so that when the hard disk is working, the operating system does not access the defective sectors.

P-List is a table with records of the coordinates of defective sectors, which is involved in the formation of the translator.
If unstable operation of a sector was detected during tests at the plant, then it is entered into the P-List table, and the rest after it are renumbered the very last sector, which no longer has enough space, is supplemented from the reserve area. The number of sectors in reserve is reduced.

Another mechanism for excluding BAD sectors from the logical space is implemented using the G-List table. This table is formed during the operation of the hard disk. If a sector is not readable, then it is placed in the G-List and a sector read error is returned to the computer. If it is written to, the hard disk management program will find it in the defects table and replace it with a healthy sector from the spare area.

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