HDD

Hard disk

Hard disk drive (HDD - Hard Disk Drive) or a computer hard drive - the main storage location (operating system, applications, data). The right information at the right time is read from the hard disk and CPU processing, the result of treatment can be recorded on a hard drive.

Hard drive1 th hard drive was invented before the release of the personal computer - in 1957 by IBM. He had a size of 5 MB and cost crazy money. For a personal computer IBM PC XT was invented disc capacity of 10 MB. The hard disk has 30 tracks and 30 sections in each lane. By analogy with the marking of a multiply carbine Winchester - "30/30", the hard drives were called "hard drive" or mean "screw".

What exactly are the system hard drive? The basis of the hard drive - power metal disks coated with a special drug that is able to perfectly keep the impact of the magnetic field (for example, iron oxide). Innovation drives contain from 1 to 3 of these drives. The discs have a good balance and very rovnenko plane as speed enough (normal speed - 7200 or 10000 rev / min), and the accuracy of the actuator must be the highest.

Written to disk using special magnetic heads (usually 2 for each disk - from two sides of the disc), capable forms the magnetic field under the current pulses. This magnetic head magnetizes the magnetic moment of the disc portion certain direction (logical "zero" or a logical "one", depending on the direction of the magnetic moment). Magnetization process proceeds by filing a current pulse at a time when the magnetic head is positioned at the right place.

To read from the disk using special magnetoresistive heads, which react to the modification of the magnetic field by changing the current excited in the head. This analog signal is read out, digitized and fed into a computer system.

Information on disks located in concentric circles - tracks. Magnetic heads in the process of moving from one track to another. In the advanced hard disk drives to move the magnetic heads used solenoid actuator. They move around its own axis. The back of the head is fixed coil that is attracted to that or the other side of the electromagnet. Since hard disk drives spin, then moving to the other side or the other, the head has access to any point on the disc. After a power failure, read heads are led away from the plane of the disc and parked. The fall of the heads on the disk plane is not allowed!

Diagram of HDD

The information on the disk is stored in the form of concentric circles. Head block is one, and all the heads are moved at once. Each head serves one side of the 1st drive. In every episode, all heads are on the same track, but on different disks. In the vertical plane of a set of paths forms a cylinder.

The track is divided into sectors. Each sector holds 512 bytes of information. Sector - the minimum element of disk space.

Probable maximum volume of information stored hard drive - is the product of 3 components: the number of cylinders, number of heads, number of sectors.

From a scientific and technical point of view, easier to manufacture hard drives with fewer drives, but with a higher density of tracks on one disc.

Should say more about such nuances as the physical location of cylinders, heads and sectors, and logical disk razmeschenie.

Physical location, we touched a little higher. However, logically (just so they "see" the computer) Setup program puts these characteristics in another (usually indicated on the cover of the hard drive), and the forthcoming computer operates with a logical breakdown of the hard drive. In order to match the physical and logical location of disc characteristics, has established a special procedure - Broadcast disk geometry. An ensemble located on the hard disk and converts logical coordinates into physical, providing access to relevant heads of the physical drive.

In the production of discs can not avoid a certain percentage of rejection sectors or even tracks (if only the disk itself provides a suitable volume). Low level formatting when disk space is divided into logical cylinders, heads, sectors, these areas are marked and the rejection is maintained given the hard drive not included.