Physical structure of a Hard Disk

These discs, whose number varies according to the capacity of the unit, are grouped on one another and traversed by a shaft and rotate continuously at high speed. Also, each disc has two tiny heads read / write, one on each side. These heads are floating on the surface of the disc without touching at a distance of about 3 or 4 micro inches (for information, you can comment that the diameter of a human hair is about 2μ inches).

These heads generate electrical signals that alter the magnetic fields of the disk, giving way to information. Depending on the direction in which the particles are oriented, it will be 0 or 1. The distance between the head and the disk platter also determine the storage density of the same, because the closer to each other, the smaller is the magnetic and can hold more information.

Between the plate and the head is an air cushion formed by the self-rotation preventing the heads from touching the disk, however, when the disc is stopped, parked on a track heads designed for that purpose by direct contact with the plate. The heads are mounted on an actuator arm that moves sideways sweep allowing the entire surface of the plate. This indicates that the heads move together, and only one can transfer data.

On the outside have a data interface to connect the device to the motherboard and plug for the power. Depending on the model may include some type of pin configuration using jumpers.

Tracks, Cylinders and Sectors

It should also discuss other aspects of the physical structure of the disk capacity and make the reading / writing data. For starters, the disk surface is divided into a series of concentric rings, called tracks. At the same time, the tracks are divided into sections of equal length, called sectors, a sector contains 512 bytes. Another concept is the cylinder, used to describe the tracks that have the same number but different disks, ie the projected concentric tracks in different dishes, makes the cylinders. Finally, the sectors are grouped into blocks called clusters or allocation units.

These concepts are important when you install and configure a hard disk, and take on greater significance when later the logical aspects are addressed, such as the file system to use. The modern mothers detected automatically installed hard drives, but formerly had to enter some values ​​one by one (always come written on a label affixed to the top of the disc), which forced her to have some technical knowledge to configure and get the most most of it. This logical structure that specifies the details of the tracks and sectors performed at the time of the manufacture of hard disk and is called Low Level Format. The size of the clusters is given by the High-Level Format will be discussed later.

As shown in Figure sectors are not the same physical size, but all have the same capacity, 512 bytes. All these divisions and conventions used to locate data within the disk, ie part of the "direction" of the data. Addressing the first system that was used is CHS (Cylinder - Head - Sector), since these three values ​​can be placed either a data disk. A piece of information may be recorded in sector 3 of the cylinder 5 of the face 4, for example. Currently using a simpler system, called LBA (Logical Block Addressing), which consists of dividing the entire disk blocks and assign each a unique number. The location of the data is done by indicating the number of the desired block (which includes one or more sectors) regardless of which side of the plate is or what track.

Multiplying the values ​​CHS each other to obtain the number of sectors on the hard disk, then if that value is multiplied by 512 will get the disk capacity in bytes. It would divide the result by 1,024 to obtain the capacity in MB or GB, but in reality most of the time the hard drive manufacturers to divisions if we get 1,000.