Data recovery base – 3. HDD mystery head, sector and cylinder
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1.1.3 tracks, sectors and cylinders
1. Track
As the disk rotates, if the head is held in a position, the surface of each head in the disk will draw a circular trajectory, the trajectory is called a circular track. These tracks can not see with the naked eye, because they are only on disk in a special way magnetized magnetized area, information on the disk is stored along this track. Between the next adjacent track is not significant, because it will affect the magnetic means spaced too close to each other when the magnetization, and also difficult to read and write heads. Each track on the disc in order from outside to inside, "0" for no.
2. Sector
Each track on the disk is divided into a plurality of arcs, the arc is a disk sector. Each sector includes storing the data segment and disk management information segment information, the disk drive 512 bytes when reading and writing data to the disk, to be in sectors, the sector from "1" to start numbering .
3. Cylinder
Hard typically consists of a set of overlapping discs. As mentioned earlier, each disk surface is divided into an equal number of tracks from the outer edge of the "0" number with the same number of tracks forming a cylinder, called the cylinders of the disk. Accessing data on the disk is carried out along the cylinder, which is sequentially written to the disk in a high number of low numbers of a cylindrical disc, and then filled with a cylinder to the next cylinder.
Disk cylinders with a number of tracks on the disk equal. Since each disk has its own head, therefore, equal to the total number of disk heads. The so-called hard CHS, which means the Cylinder (cylinder), Head (head), Sector (Sector), shown in Figure 1.6.
 Figure 1.6 tracks, sectors and cylinders schematic
 For different hard drive, the physical location of the firmware zone is different, some located closer than "0" tracks the outer edge of the track on the disk slice that we often say "negative track." Some in the middle of a disk slice, the number and function of the program recorded there are differences. Due to the production process can not be guaranteed to be completely consistent throughout the disc, there must be a small part of the sector can not be stable reading and writing data, which is what we call bad sectors.
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