Hard disk, data and restore data

There are very few people who have seen a hard disk. Unlike the floppy disk drive are so delicate that must be constantly in a protective aluminum.

Everything you see is a box of metal with some circuits. There is no easy way to access the box to see the disk: open the disc means the contamination.

The units were opened only in clean rooms or rooms where workers wear clothes surgeon and the air is not filtered to contain dust particles. Some discs are included in removable cartridges that are inserted into units, but most are not removable.

IBM invented the disk drive is not removable small and has called Winchester (apparently, because the number of coincided with the model number of a popular Winchester rifle).

Runs, sectors and heads of the hard disk.

Despite all this impressive armour, a hard disk is not very different from a floppy. The data are recorded in written form of magnetic flux in a circle around the ring central disk.

Each of concentric circles form a track and each track is divided into an equal number of segments called sectors. The head read / write moves dall'anello external disk toward the center, stopping above the track which contains the information required by the computer.

Once in the right position, the head expects that the industry is correct to below it, then law or write data in the field. C

Hard Drive, CDs, DVDs, diskettes.

Hard disks are different from other storage media for the density with which data are recorded on the surface of the disk, and the speed with which they operate.

Unlike other media, the hard disk can store up to ten times more data on each track. Because of this density of data is necessary to head a head of read / write very small and very close to the surface of the disk.

Any flexibility of hard disk would jump and beat head read / write. For this reason the disc is made of a hard surface and rigid using slabs of aluminum coated with magnetic material.

The dishes on the hard disk.

In order to improve the capacity most of the hard drive contains two or more disks. The discs, which are commonly called plates, are mounted around an axis called "spindles." All dishes rotate at the same time.

The engine's moving plates can be incorporated in the "spindles", or it may be placed below the "spindle". Both sides of the plate contain data.

Since it would be impractical for a head reading / writing work for all sides of the dishes, each side of the pot has its head. The heads are grouped in a frame-shaped comb that moves them all at once. The accuracy of this mechanism is impressive. Food and heads must match exactly in every position of every track, being all head to a hundred-thousandth of an inch of the surface of the pot. This geometry both states remains even when the heads are in motion, and asserts back along the surface of dishes, which rotate at high speed. Truly high-tech.

The heads may be close to flat, without touching, because actually fly on the surface because of air flow created by the rotation of the disc. The head rose slowly when the drive begins to move and land without problems when you cut off the flow of current and dishes and they reduce their speed to stop. When the appliance is not working, heads resting on the surface of the disk.

The disk drives are connected to the IDE port on the motherboard, so that when the data are read from the surface of the disc they pass by the heads circuits controller. As we shall see later, not all drive need a controller that acts as an intermediary between the unit and the computer.

The data sent from the surface of the disk controller reach the buffer, a small area of which function as temporary storage for data. Once transferred data in the buffer, the controller sends a signal to the microprocessor to begin the transfer of data to memory chips.

Hard disk UDMA

The data are transferred using one of two following techniques: first in the first computer on the market was the chip to do the work, but currently is used direct memory access (DMA Direct Memory Access).

The DMA has a special chip that moves data directly from the memory controller in a single step, rather than implement the two-step process that requires the transfer to the first microprocessor and then to memory.

Then the data can be found in system memory, in areas that were reserved for the "buffer". The number of "buffers" and its size is configurable depending on the operating system and application requirements.

To write data, the whole process is reversed. The application tells the system where the data in memory. The system moves to "buffer" and initiates the DMA for the transfer to the disk controller. Then the disk driver starts to write.