Storing information on hard drives

Part 1

1. Introduction

Most users, answering the question of what is in their system unit, among other things, mention the hard drive. Winchester is the device on which your data is most often stored. There is a legend explaining why hard drives have such a fancy name. First HDD, released in America in the early 70s, had a capacity of 30 MB of information on each work surface. At the same time, the O. F. Winchester magazine rifle, widely known in the same America, had a caliber of 0.30; maybe the first hard drive rumbled during its work like an automatic machine or it smelled of gunpowder - I don’t know, but since then they began to call hard drives hard drives.

Failures occur during the operation of the computer. Viruses, power outages, software errors - all this can cause damage to the information stored on your hard drive. Damage to information does not always mean loss of it, so it is useful to know how it is stored on the hard drive, because then it can be restored. Then, for example, if the boot area is damaged by a virus, it is not at all necessary to format the entire disk (!), but, after restoring the damaged area, continue normal work with the preservation of all your priceless data.

On the one hand, in the process of writing this article, I set myself the task of telling you:

1. about the principles of recording information on a hard disk;
2. on the placement and loading of the operating system;
3. about how to competently divide your new hard drive into sections in order to use several operating systems.

On the other hand, I want to prepare the reader for the second article, in which I will talk about programs called boot managers. In order to understand how these programs work, you need to have a basic knowledge of things like MBR, Partitions, etc.

Enough general words - let's get started.

2. Hard disk device

3. Information storage

Unfortunately, quite often there is confusion between such concepts as "sector", "cluster" and "block". In fact, there is no difference between a "block" and a "sector". True, one concept is logical, and the second is topological. A "cluster" is a number of sectors considered by the operating system as one. Why didn't they abandon simple work with sectors? I will answer. The transition to clusters happened because the size of the FAT table was limited, and the size of the disk increased. In the case of FAT16, for a 512 MB disk, the cluster will be 8 KB, up to 1 GB - 16 KB, up to 2 GB - 32 KB, and so on.

In order to uniquely address a data block, all three numbers must be specified (cylinder number, sector number on the track, head number). This method of disk addressing was widely used and was subsequently designated by the abbreviation CHS (cylinder, head, sector). It was this method that was originally implemented in the BIOS, so subsequently there were restrictions associated with it. The fact is that the BIOS has defined a bit grid of addresses into 63 sectors, 1024 cylinders and 255 heads. However, the development of hard drives at that time was limited to the use of only 16 heads due to the complexity of manufacturing. From here appeared the first restriction on the maximum allowable for addressing capacity hard disk: 1024×16×63×512 = 504 MB.

Over time, manufacturers began to make larger HDDs. Accordingly, the number of cylinders on them exceeded 1024, the maximum valid number cylinders (in terms of older BIOSes). However, the addressable part of the disk continued to be 504 MB, provided that the disk was accessed using the BIOS. This limitation was removed over time by the introduction of the so-called address translation mechanism, which is discussed below.

The problems that arose with the limitation of the BIOS in terms of the physical geometry of disks eventually led to the emergence of a new way of addressing blocks on a disk. This method is quite simple. Blocks on the disk are described by one parameter - the linear address of the block. Disk addressing linearly received the abbreviation LBA (logical block addressing). The linear address of a block is uniquely related to its CHS address:

lba = (cyl*HEADS + head)*SECTORS + (sector-1);

The introduction of linear addressing support in hard disk controllers made it possible for the BIOS to take up address translation. The essence of this method is that if you increase the HEADS parameter in the above formula, then fewer cylinders will be required to address the same number of disk blocks. But then more heads will be needed. However, only 16 out of 255 heads were used. Therefore, the BIOS "s began to transfer excess cylinders into heads, reducing the number of some and increasing the number of others. This allowed them to use the entire bit grid of heads. This pushed the limit of the disk space addressed by the BIOS to 8 GB.

It is impossible not to say a few words about Large Mode. This mode of operation is designed to operate hard drives up to 1 GB. In Large Mode, the number of logical heads is increased to 32, and the number of logical cylinders is halved. In this case, accesses to logical heads 0..F are translated into even physical cylinders, and accesses to heads 10..1F are translated into odd ones. A hard drive marked in LBA mode is incompatible with Large mode, and vice versa.

A further increase in the addressable volumes of a disk using the old BIOS services has become fundamentally impossible. Indeed, all parameters are used according to the maximum “bar” (63 sectors, 1024 cylinders and 255 heads). Then a new extended BIOS interface was developed, taking into account the possibility of very large block addresses. However, this interface is no longer compatible with the old one, as a result of which old operating systems, such as DOS, which use the old BIOS interfaces, could not and will not be able to overstep the bounds of 8GB. Almost all modern systems no longer use the BIOS "ohm, but use their own drivers to work with disks. Therefore this limitation does not apply to them. But it should be understood that before the system can use its own driver, it must at least load it. Therefore, at the stage bootstrap any system is forced to use the BIOS ". This causes restrictions on the placement of many systems beyond 8GB, they cannot boot from there, but they can read and write information (for example, DOS which works with the disk through the BIOS).

4. Sections, or Partitions

During computer boot, the BIOS loads the first sector of the head partition (boot sector) at 0000h:7C00h and transfers control to it. At the beginning of this sector is the bootloader (boot code) that reads the partition table and determines the bootable partition (active). And then everything repeats. That is, it loads the boot sector of this partition to the same address and again transfers control to it.

Sections are containers for all their content. This content is usually the file system. From a disk point of view, a file system refers to a block layout system for storing files. After the file system is created on the partition and the operating system files are placed on it, the partition can become bootable. The boot partition has in its first block a small program that loads the operating system. However, to boot a specific system, you must explicitly start it. boot program from the first block. How this happens will be discussed below.

Partitions with file systems must not overlap. This is due to the fact that two different file systems each have their own idea of ​​the location of files, but when this location falls on the same physical location on disk, there is a conflict between file systems. This conflict does not occur immediately, but only as the files begin to be placed in the place on the disk where the partitions intersect. Therefore, you should be careful about dividing the disk into partitions.

In itself, crossing sections is not dangerous. It is the placement of several file systems on overlapping partitions that is dangerous. Partitioning a disk does not mean creating file systems. However, the very attempt to create an empty file system (that is, formatting) on ​​one of the intersecting partitions can lead to errors in file system another section. All of the above applies equally to all operating systems, not just the most popular ones.

The disk is divided into sections programmatically. That is, you can create an arbitrary partition configuration. Partitioning information is stored in the very first block of the hard drive, called the Master Boot Record (MBR).

5. MBR

Everything that is located at offset 01BEh-01FDh is called the partition table. You can see that it has four sections. Only one of the four partitions has the right to be marked as active, which will mean that the boot program must load the first sector of this particular partition into memory and transfer control there. The last two bytes of the MBR must contain the number 0xAA55. Based on the presence of this signature, the BIOS verifies that the first block was loaded successfully. This signature was not chosen by chance. A successful check of it allows you to establish that all data lines can transmit both zeros and ones.

The boot program looks through the partition table, selects the active one, loads the first block of this partition and transfers control there.

Let's see how the partition descriptor works:

From the point of view of disk partitions, MS-DOS has been and remains the most popular until recently. It takes into its use two of the four partitions: Primary DOS partition, Extended DOS partition. The first one, (primary) is a normal dos C: drive. The second is the logical drive container. They all hang out there in the form of a chain of subsections, which are called like this: D:, E:, ... Logical drives can also have foreign file systems that are different from the DOS file system. However, as a rule, the heterogeneity of the file system is due to the presence of another operating system, which, generally speaking, should be placed on its own partition (not extended DOS), but the partition table is often too small for such antics.

Let us note one more important circumstance. When DOS is installed on a blank hard disk, there are no alternatives in choosing operating systems at boot. Therefore, the bootloader looks very primitive, it does not need to ask the user which system he wants to boot. With the desire to have several systems at once, it becomes necessary to start a program that allows you to select a system to boot.

6. Conclusion

Many thanks for the help to Vladimir Dashevsky

Exam case.
Professor. How does a transformer work?
Student. Woo-o-o-o-o-o-o-o-o-o-o-o...

We have long been accustomed to personal. We turn them on and work, in fact, without thinking a little about how they are arranged and how they work. All this is due to the fact that PC developers and software developers have learned to create reliable products that do not give us a reason to once again think about the design of a computer or programs serving it.

However, readers of the blog are probably interested in learning about how computers and software work. This will be the subject of a series of articles that are published under the heading "How a PC Works".

How a PC Works: Part 1: Processing Information

Computer for automating information processing processes. It is arranged accordingly in order to have all the possibilities for the successful fulfillment of its mission.

In order to process information in a computer, it is necessary to do the following basic operations with it:

– enter information to computer:

This operation is needed so that the computer has something to process. Without the possibility of entering information into a computer, it becomes, as it were, a thing in itself.

– store entered information in computer:

Obviously, if you give the opportunity to enter information into a computer, then you need to be able to store this information in it, and then use it in the processing process.

– process the entered information:

Here it must be understood that certain processing algorithms are needed to process the entered information, otherwise there can be no talk of any information processing. The computer must be equipped with such algorithms and must be able to apply them to the input information in order to "correctly" convert it into output data.

– store processed information,

As well as with the storage of the entered information, the results of its work, the results of processing the input data, must be stored in the computer so that they can be used in the future.

– output information from a computer:

This operation allows you to display the results of information processing in a readable form for PC users. It is clear that this operation makes it possible to use the results of information processing on a computer, otherwise these processing results would remain inside the computer, which would make their receipt completely meaningless.

The most important skill of a computer is the processing of information, since its beauty lies precisely in the fact that it can transform information. The entire device of a computer is due to the requirement to process information in the shortest possible time, most fast way.

Information processing on a computer can be understood as any action that transforms information from one state to another. Accordingly, the computer has a special device, called , which is designed exclusively for extremely fast data processing, with speeds reaching billions of operations per second.

CPU

The processor receives (takes) the data required for processing from a device designed for temporary storage of both input and output data. There is also a place in the RAM for storing intermediate data formed in the process of information processing. Thus, the processor both receives data from RAM and writes the processed data to RAM.

Random Access Memory (RAM)

Finally, for input and output of data, they are connected to a computer, which allow you to enter information to be processed and display the results of this processing.

External hard drive, external DVD device, flash drive, keyboard, mouse

The processor and RAM work at the same speed. As mentioned above, the speed of information processing can be many millions and billions of operations per second. No external input and output device can operate at such speeds.

Therefore, for their connection to the computer, special I/O device controllers. Their task is to match the high speeds of the processor and RAM with relatively low speeds input and output of information.

These controllers are divided into specialized, to which only special devices can be connected, and universal. An example of a specialized controller device is, for example, a video card that is designed to connect a monitor to a computer.

Any computer must have devices that store information. Information storage devices in a computer are divided into RAM (memory, which is needed to store intermediate results of calculations) and long-term - files are stored here (the definition is rather rough, but it reflects the essence correctly).

In a computer, any information is stored only until the computer is turned off. If you need to save a document and come back to work on it tomorrow, you need to write it to a durable storage device, usually a disk. Here are the most common types of drives and storage devices.

1. Floppy disks: 3.5-inch 1.44 MB floppy disks were once the "ubiquitous" medium for storing information, but now they are hopelessly outdated. You can consider that a drive for them in your computer is optional. This is how she looked.

2.SD memory cards/xD/MS: Even now, after floppy disks have disappeared from the scene, many computer cases have a bay dedicated to installing floppy drives. Why not install a memory card reader in this compartment? With this reader, you can read data from memory cards for cameras (and write too). Devices for working with memory cards (card readers - literally "card reader") are very inexpensive, and ordinary card readers will allow you to work with many different cards - SD, xD, CF, Memory Stick, etc.

3., or hard drives: buy the largest hard drive you can afford. Digital photos always take up more space than you'd expect, and your son's music collection probably takes up more space than the entire CIA archive. Although it is generally believed that more expensive hard drives are more reliable than cheaper ones, individual results vary and it is difficult to say anything for sure.

Performance, i.e. the speed at which a hard drive writes and reads data is less important than capacity. Speed ​​will become more important if you regularly work with large amounts of data, such as video recordings. However, it is worth considering buying a hard drive with a new interface for a few extra dollars, this interface is quickly replacing the outdated and slower IDE (also known as ATA or PATA). In addition, SATA cables are narrower and more flexible than wide and awkward IDE cables.
Also pay attention to external hard drives, which are usually connected to the computer via a USB cable (). They run almost as fast as internal hard drives and can be plugged in and out of your computer as needed. In addition, they do not contribute to the heat that is in the computer case.
If you are buying a new hard drive, have the dealer install it in your computer. At installation of hard disk, you need to pay attention to a number of little things that are obscure to a non-specialist.
4. CD and DVD drives: these drives allow you to read and write discs with various information (from text documents to music and video) on ordinary compact discs (CD) about 700 MB of data is placed; DVDs hold about 4.5 GB, and dual-layer DVDs hold about 8 GB. Don't be greedy - buy yourself a drive that supports dual layer DVDs (DVD+RW DL), even if dual layer discs are expensive. If you don't know how to install this drive, buy yourself an external USB option - Windows works great with these drives.

Many older CD players (for example, in music centers or car stereos) cannot read rewritable discs (CD-RW). These drives require a CD-RW (Write-once CD).
If you want to burn CDs or DVDs on a new computer and then play them on devices that you already have, it is better to burn a test disc before buying and see if it plays normally. Many cheap DVD players can easily handle discs full of MP3 music. However, there are models, and among the expensive ones, that do not perceive such discs at all. The only way to test the capabilities of your player is to experiment.
5. USB flash drives : wonderful things! The size of a pack of chewing gum and yet capable of holding a sea of ​​​​data. There are flash drives with a capacity of 16 GB or more - these are several DVDs. In addition, these devices are not afraid of shock and magnetic fields, and the ability to connect via USB port means a minimum of fuss with them when transferring data between different computers. Windows detects such a drive as soon as it is connected to USB port. When choosing such a flash drive of a certain size, take the cheapest one: more expensive models of the same size usually add little-used features.

The article is very well written plain language. Experienced computer users may skip the text.

About information and computer disks

You have heard that there is a lot of information inside a computer. That a computer can "surf the Internet", store "pictures", run games, print texts, and there are "some programs" in it.

In general, this is correct. But there is something else that needs to be known to make it easier to understand the essence.

When we turn on the computer, we can see some inscriptions on the screen, changing pictures, flashing rectangular frames, and so on. Where this is all taken? All computer content (texts, photos, music, movies, programs, games) is called " information". It is stored inside the computer.

But where exactly is all this located? Look at your computer. Think .. scratched with a carnation on the back cover? No. On small pieces of paper, rolled up and stuffed into a hole from the bottom? Hardly.

The information in a computer is stored on a special such device, in such a small iron box, with the name "disk"

Disk- this is such a special device, "device", "box" - designed to store all the information that is already on the computer. So, we have a computer, and inside the computer disk, on which is stored information.

For many who are still new to computer matters, the concept is information - pretty blurry. Let's make it more specific so that it's easier for us to discuss everything else. Imagine that you have a paper notebook in which you wrote down the birthdays of your friends, relatives and everyone you care about. Once a week, you look through this notebook and say to yourself: "So .. you must not forget to congratulate your friend Vasya on his birthday, in two days." And another time: "Oh! I almost forgot. Tomorrow is my pet parrot's birthday. I need to buy him something tasty."

I want to say that the contents of your notebook are what they are. information. You looked through it (searched it) - and made the necessary conclusions. And no one was forgotten to congratulate on time. Now imagine - the lines from your notebook appeared on the computer screen. Let you not yet know how they got there, but you can imagine it. And now, instead of a notepad, you read the inscriptions on the screen. And now on the screen, instead of a notebook, the dates of birth of Vasya's friend, Kesha's parrot or the Minister of Finance of Honduras are recorded. What does this mean?

That even in Honduras there is finance. It's a joke. Actually this means that information, which you are accustomed to and which used to be in your notebook is now stored in your computer. Where exactly is it stored on the computer? Right! On disk.

You heard that you can watch movies on your computer. What is a film? That's right, that too information. On the computer, you can listen to music - this is also a kind information. Only this information is for your ears. On a computer, you can view photos - this is information for your eyes.

Let's conclude: Everything that you can see on a computer screen or hear from a computer is INFORMATION.

Learn more about information storage

I told you that information in a computer is stored on a disk. In fact, the word "disk" refers to various technical devices, various technical "things" that can be permanently inside the computer, or can connect to it from time to time, and then turn off. All these devices have one thing in common - they store inside themselves information. And they allow the computer to which they are connected to extract this information into the light.

For example, if you have a laptop or desktop computer, then inside, as a rule, there is HDD. This is really some kind of very useful metal box that is hidden inside the computer case. It can only be seen if you open the inside of the computer. It is installed inside permanently, the computer needs it, on it it stores important information, which is required so that the computer can generally turn on and start working. But in addition to important computer information, HDD allows you to store your favorite photos, movies, music, e-books and so on. How much free space is enough.

Let's get into the technical details a little more. A little bit. I said that the hard drive is a metal box. But what is inside this box? And why is the box called - a hard drive - if it is not a round object at all, but a rectangular one?

The fact is that inside this box there really is a disk, a metal one, it really rotates with a motor that is hidden inside this box. Do you remember the vinyl records with the recordings of the Orera ensemble or the master of the Soviet patriotic song Iosif Kobzon? Here, the inner round "plate" of the hard drive is somewhat reminiscent of a record with a melody. The purpose of both of them is to store recorded information. I hope you understand that the melodies on a vinyl record can be called information.

Imagine being lucky today. You managed to buy a record with new songs by "Syabrov" in a village store. But if you don't have a player, a gramophone, into which you can put this record, you won't be able to enjoy the music. All you have to do is spin the record on your finger and sing along. This means that in addition to the disc (record) itself, we also need a device that will play the disc. Let's put it scientifically. We have "information carrier" disc, disc. To use this information (listen to music) - we need "reader" information - player.

So here it is HDD(a box inside the computer) contains both a "media" and a "reader". If we take a vinyl record and glue it permanently to a record player, we have a hard drive. The storage medium, in this case, is inseparable from the reading device. Therefore, it is impossible to pull out a round plate on which information is recorded from a hard disk. He will break, so he - NON-REMOVABLE.

But there are also REMOVABLE storage devices. Have you ever seen an optical disc? They are also called DVD ("di-vi-di") disks, CD ("si-di") disks. Now on such disks they sell music, films, computer games. Information is recorded on the plastic disc itself, but the reader (player) is located separately. For example, it is built into a computer and has a narrow slot on the side. You can insert the desired optical disc into this slot, watch a movie, then pull out this disc, insert another one - with a new movie. In this case, we see that an optical disc reader is a separate "thing", and the information that this device can play is located on optical discs called DVDs or CDs. These discs are usually stored on a cabinet shelf, in plastic boxes.

Even a computer has a built-in floppy disk reader. This is a separate type of disk. These discs can also be inserted and removed from the computer. A small amount of information is placed on such a disk, so such disks are becoming obsolete. On many modern computers and laptops do not have a floppy disk reader.

So. Let's paint a short picture of what has been said. We have a computer with a hard drive inside it. Which cannot be pulled out, it is always inside the case. It has information on it. This is clear? But at the same time, a DVD drive can also be located inside the computer, with a slot on the side where you can insert any optical disc. There is no information in the DVD reader itself, but if we insert an optical disc into it, the information will appear. The device will be able to read the information from the disk we inserted. Thus, we will have two storages of information in our computer at the same time: a hard drive and a DVD drive with some disc inserted into it (with a new computer game, for example)

To be continued...

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RAM- memory designed for temporary storage of data and commands necessary for the processor to perform operations. Random access memory is made in the form of memory modules (flat plates with electrical contacts, on the sides of which large integrated memory circuits are placed). RAM modules have a large number of indicators (type, type, timings, frequency) that significantly affect the operation of the memory.

During operation, the computer's memory refers to one of two types of so-called "stores" of information. Computer volatile memory RAM (Random Access Memory)- this is such a repository of information that must be constantly updated so that it stores various information needed in this moment for computer operation. It is automatically cleared when the computer is powered off.

Computer static memory ROM (Read Only Memory)- this is an information storage designed for permanent and long-term storage of files that should be in the computer's memory after the computer is turned off from the power supply.

External (long-term) memory - this place long-term storage data (programs, calculation results, texts, etc.) that are not currently used in the computer's RAM. To work with external memory, you must have a drive (a drive - a device that provides writing and reading information) and a storage device - a carrier. Devices are usually divided into types and categories in connection with their principles of operation, operational, technical, physical, software and other characteristics.

Flexible magnetic disks . Removable magnetic disks (floppy disks) are inserted into the computer through a special slot system block- disk drive. In fact, this is not one disk, but a group of disks that have a magnetic coating and rotate at high speed. The main parameters of floppy disks are: technological size (measured in inches), recording density (measured in multiples) and full capacity.

Hard magnetic disks or HDD, hard drive, - the main storage of information of large volumes, based on the principle of magnetic recording, is hidden inside the case of the system unit. It is the main storage medium in most computers. Information in the HDD is recorded on hard plates coated with a layer of ferromagnetic material. The storage medium is combined with a drive, drives, an electronics unit, and is usually installed inside a computer system unit.

External rigid discs– dynamic data storage systems. They are convenient when doing business, provide freedom of creativity, interaction at any time, anywhere.

The external hard drive is easy to use due to its portability, support high-speed interface for fast data transfer.

Optical drives and discs. The collective name for information carriers made in the form of disks, reading from which is carried out using optical radiation. Disks are usually flat, their base is made of polycarbonate, on which a special layer is applied to store information. To read information, a laser beam is usually used, which is directed to a special layer and reflected from it.

Laser drives and disks. Laser disk drives (CD-ROM and DVD-ROM) use the optical principle of reading information. Laser CD-ROM (CD - CompactDisk, compact disc) and DVD-ROM (DVD - Digital Video Disk, digital video disc) stores information that was recorded on them during the manufacturing process. Sign up for them new information impossible, which is reflected in the second part of their names: ROM (ReadOnlyMemory - read only). Such disks are produced by stamping and have a silver color. On CD-RW and DVD-RW (RW - ReWntable, rewritable) discs, which have a "platinum" tint, information can be written multiple times.

The first generation of optical discs: laser disc, compact disc, magneto-optical disc.

Second generation of optical discs: DVD, MiniDisc, Digital Multilayer Disk, DataPlay, Fluorescent Multilayer Disc, GD-ROM (Compact Disk Read-Only Memory), Universal Media Disc.

The third generation of optical discs: Blu-rayDisc, HDDVD, Forward Versatile Disc, Ultra Density Optical, Professional Disc for DATA, Versatile Multilayer Disc.

Fourth generation of optical discs: HolographicVersatileDisc, SuperRensDisc.

Flashmemory. Flash memory is a non-volatile type of memory. It is a microcircuit placed in a miniature flat package. To read or write information, a memory card is inserted into special drives built into mobile devices or connected to a computer via a USB port. Flash-memory cards do not contain moving parts, which ensures high data safety when used in mobile devices (portable computers, digital cameras, etc.). There are a lot of them: SD, MMC, CompactFlashType I and II, MemoryStick, MemoryStickDuo, TransFlash, miniSD, microSD, RS-MMC, SmartMedia, MiniDisk, etc.

compactFlash- perhaps the oldest flash memory: the first copy was released back in 1994 by SanDisk. In total, there are two types of CompactFlash cards: CF Type I, CF Type II, and they differ only in the thickness of the case.

SD (SecureDigital)- was also created by the efforts of SanDisk, Panasonic and Toshiba. These cards use cryptograms (data encryption) to protect data from unauthorized copying or overwriting.

MMC (MultiMediaCard)- is the fruit of the work of SanDisk and Siemens. Each MMC has its own memory controller. At the same time, the thickness of multimedia cards is almost a third less than that of the "spy" brother, which allows the use of MMC drives in various miniature devices.

RS-MMC (ReducedSize MMC)– also known as MMCmobile. They differ from MMC only in reduced dimensions and are used mainly in mobile phones.

Memory Stick Duo– is an evolution of the Memory Stick itself. The size and power consumption of cards have decreased, but at the same time, the maximum capacity has also decreased. The rest is completely similar to the usual MS.

smart media- a standard that was developed by Toshiba back in 1995. Features this standard can be considered very low power consumption and the lack of its own controller, the speed is extremely low and the maximum memory capacity is only 256 MB, which is negligible by today's standards, especially considering the size of the card

ХDPicture (ExtremeDigital)- were created by FujiFilm and Olympus to replace the outdated SmartMedia format. The cards are used primarily for digital cameras these companies.

Also recently, USB flash drives (“flash drive”, USB drive, USB disk) have become widespread, practically replacing floppy disks and CDs.

Storing information online

The Internet is the union of computers around the world into a single information network. In another way, the Internet is called the world computer network.

To connect computers use the usual telephone lines and a modem device. The modem converts the information to a form suitable for transmission by telephone.

Thus, information stored around the world becomes available to anyone who has a computer, telephone and modem.

Telephony is not the only way to connect computers. Much faster information is transmitted via optical cables and radio communications. These channels are gradually replacing telephone connections on the Internet.

On the Internet, you can find the answer to almost any question. Read the latest newspaper, look into the library, book plane tickets, buy goods, make pen pals.

We know that programs and data in a computer are stored on the hard drive as files.

File- this is a certain amount of information that has a name and is stored in long-term (external) memory.

File name- a sequence of characters that allows the user to navigate the file system. A file name consists of two parts separated by a dot: the file's own name and an extension that specifies its type. A custom filename can contain from 1 to 255 characters. In addition to Latin, the use of the Russian alphabet is allowed.

Extension is a combination of letters and numbers from one to three characters long, which complements the name itself, but more often indicates the format and type of data stored in the file. It is separated from the actual file name by a dot and is an optional part of it. Extensions are used to identify the type (format) of a file. With their help, the user software The computer can determine the type of data stored in the file.

It is customary to specify the extension as *.rar, i.e. an asterisk and a dot are added before the extension characters, where the asterisk symbolizes any file name.

The extension can indicate not only the type of information that is stored in the file (image, media file, text file), but also on the way this information is encoded. For example, *.gif, *.jpg, *.bmp, *.raw, *.png, etc. are image file extensions, but the image encoding methods in such files are different, and not every program that opens one type will be able to open another.

There are files that do not have an extension, usually this system files.

The file is opened by the program in which it was created, or by a universal program.

File extension examples different types:

*doc, *, xdoc, *.rtf, *.txt, *.pdf - text documents(the content of such files is text and they are opened in a program for working with text - Letter.doc, Catalog.xls, text.txt).

*.jpg, *.gif, *.jpeg, *.bmp, *.raw, *.png, *.emf, *.ico, *tif, *.tiff, *.jp2, *.pcx, *.tga , *.wbmp - graphic image (photos and pictures - Drawing.gif, Nature.tif, Photo.jpg, Drawing.bmp).