External computer memory

The theme of our today's article is the external memory of a computer. But first I would like to say a few words about one error, which turned out to be incredibly "tenacious". Back in school in computer science lessons, when studying the internal arrangement of the system unit, among other things one necessary component is indicated - RAM. Physically, it is represented by microcircuits, soldered on a textolite strip with two rows (a comb) of sliding contacts, which are connected to the motherboard connector. For example, when they say that there is not enough memory, they mean a small amount of RAM. Either common, or for some kind of application. However, sometimes the term "external memory" is used. This is incorrect, if only because, for example, it is unlikely anyone will come up with the idea to call the book "memory." A book is a carrier of information, and memory is something completely different.

What do some mean by the term "external memory"? The above RAM has a significant drawback, which manifests itself in the loss of all the data recorded in the microcircuit cells with each power failure. Therefore, it is used by computer nodes only with the current calculations, and for long-term storage of information , external memory is used. It's a hard drive, a USB flash drive, a CD-ROM drive, even a printer, with a number of reservations. That is, all those devices in which the safety of the recorded data does not depend on the availability of electricity.

All user files, including the operating system itself, are stored on such media. Compared with the RAM, these devices have a much larger volume, and in some cases almost unlimited. For example, if the capacity of the modern average computer is 4-8 GB, then the hard drive is rarely less than 250 GB. Using removable media (CDs) to store files, you can, theoretically, save an infinite data stream.

External memory is physically represented by drives with different operating principles. One of the first such solutions were diskettes. A flexible polymer base in the form of a disk was covered with magnetic spraying, the surface of which was magnetized in a special way by the recording head of the drive. The principle is almost the same as in the old cassettes for audio and video devices.

Almost simultaneously, there were more advanced design solutions, called hard drives. In the body were placed several inflexible disks of non-conductive current material, covered with a magnetic layer. Since the recording head did not touch directly with the surface, "flying" on the airflow, it was possible to significantly increase the rotational speed of the disks, and hence the productivity of the entire device.

A completely different principle of operation is used in drives for reading / writing CDs. At the command of the computer, the laser beam, in a certain way, presses depressions in a thin metal. When reading, the same ray is reflected from the mirror substrate layer, captured by the photocell and analyzed. Thus, the recorded information is restored.

These are just some types of storage devices. By the way, at the time of the first 8086 computers there was a solution, which rightfully can be called external memory. These were modules for expanding the main volume of the RAM, inside which the chips were located. The difference from modern slats is that the device was truly external.