Computer Hard Drive
The hard disk of the computer (it's also HDD (Hard Disk Drive), it's also a hard drive, it's also a magnetic drive, it's also a "screw" and "hard"). Nonvolatile storage of our collections of films and other files :) "Energy-independent" in this case means that all the stored information remains on the hard disk after the computer power-off.
What are the functions (besides directly storing our data) is the hard drive of the computer? We install all our software on it. It also installs our most important program (set of programs) - the operating system. Without an operating system, a computer is a heap of expensive hardware, you understand :) The hard drive of a computer also very often performs another important function, being (if necessary) an extension for the computer's RAM. Especially - with a lack of the latter.
I will explain by example: The software running on the computer and performing a task requires 300 megabytes of memory to work, and only 250 are currently free (for example). The operating system makes a cunning move: it begins to "dump" from the RAM long-unrequested data on the hard drive of the computer, thus freeing up space in RAM for the needs of the running program.
It is fair to say that the overall speed of any task in this case begins to fall catastrophically. And this is logical. Because the speed of memory and hard drive are not in any comparison. The hard drive of the computer is much slower and the more data the operating system has to "dump" from the fast RAM, the more noticeable will be the overall performance drawdown.
If you raise this process to the extreme, then a situation is possible in which practically any user action will be accompanied by convulsive attempts of the operating system to free up the next section of RAM and rewriting the next portion of data on the hard disk. This can be visually detected by constantly flashing red indicator of the hard drive on the front panel of the computer. The result is a very slow response of the system to any user actions (often resembles hang-up) and a constantly flashing red light bulb (LED) of the hard drive on the front panel of the case .
The situation described above is often typical for computer systems with insufficient amount of RAM. More precisely, we formulate this as follows: with insufficient memory for tasks that are put before it :)
A few words about the confusion associated with the hard drive of the computer: many believe that inside it is a vacuum, but it is not. The internal closed space of the disk (hermetic block) during the production cycle is filled with air with a pressure of one atmosphere to create an air cushion effect between the pancakes and the reading and writing magnetic heads.
Requirements for air purity inside the hermetic unit (hermetic zones) are quite strict. There should be no dust particles more than 0.3 μm (micrometer or micron). For comparison, the thickness of a human hair is on average 40 μm. Now, I think, it's clear that the computer's hard drive can not be disassembled at home.
Inside the hard drive there is a spindle (axis) on which one or several magnetic disks of "pancakes" are strung, which are placed one above the other. Under this design is located the engine, which untwists the spindle to the required speed.
Magnetic heads that perform read-write operations in the computer's hard drive are combined into a magnetic head unit (MAG), which simultaneously moves them all and disposes them above the desired hard disk cylinder. The drive of the BMG is called a positioner.
And now let's "look under the cap" :) So - the hard drive of the computer without a protective cover.
What we see here:
1 - spindle, which untwists the hard drive plate.
2 - the magnetic plate of the hard drive itself is a "pancake" (where all our information is recorded)
3 - the reading-recording head, which, moving a few microns from the surface of the disk and performing read-write operations.
If we completely disassemble the hard drive of the computer, we will see the following picture:
There is another class of devices - external hard drives. It is, in fact, structurally the same hard drive, only more compact and hermetically packed in an anti-shock shell. Such drives are connected to the computer via the USB interface and act as "big flash drives" :)
There is an opinion that there is a vacuum inside the disk, but it is not. Each hard disk of the computer has a special micro-hole, under which (on the inside) are several filters, and they protect the hard disk of the hard drive from getting into it dust particles from the air.
Now in a fashion more and more solid-state computer disks enter: SSD - solid-state drive. More details about them are written in this article .