What are file archives for? File archives
Archive is a file containing one or more other files, as well as metadata. Archives are used to combine any number of files into single file- a container for the purpose of convenient storage and transfer of information or simply to compress data. To create archives and work with them, archiver programs are used.
The archives may preserve the directory structure, contain service information for detecting and correcting errors, comments and other information. Depending on the archive format, the data in it can be encrypted using a password.
Application
Archives are especially useful as a way to package file system data and metadata into a single file for storage on a computer or for transfer over channels that only support file-by-file transfer, such as transfer of directory structures over e-mail.
In addition to archiving purposes, archives are often used to distribute software packages; in this case, the archive is often called a distribution package and can be applied to additional conditions regarding the content (say, a manifest file must be present). Examples of distribution archives: deb for Debian, JAR for Java, APK for Android.
Functional Features
Depending on the type, archives support combining files into one, data compression, encryption, multi-volume (archive of several parts), checksums to verify the integrity of archive contents, self-extracting, self-installing, source volume and media information, directory structure information, notes and comments, and other metadata. The archive file format is determined by the file extension and/or file header. Archivers and authoring software are used to create archives. optical disks and programs for working with disk images.
Archive formats
Archive format- This file format archive file. There are many archive formats, but only a few have received widespread acceptance and support from software vendors and user communities. So, among the most popular in Windows environment include ZIP, RAR, 7z, and on Mac OS - the SIT format.
Archive types
- Archiving only formats only merge files into one (example: tar).
- Compressive only formats only perform file compression (examples: gzip, bzip2).
- Multifunctional formats allow you to merge files into one, compress them, encrypt them, create information for detecting and correcting errors, design archives as self-extracting to extract content without the participation of additional software (examples: RAR, ZIP,).
- Distributive formats are used to create software installation packages, which can also be self-installing files (examples: JAR, APK, IPA).
- Formats disk images used to create disk images used as information storage volumes (examples: ISO, NRG).
Subtypes of archives
Self-extracting archives
Self-extracting archives are often also called SFX archives (from the English SelF-eXtracting - self-extracting). Unlike a regular archive, a self-extracting archive has an executable file format (in Windows it is a file with the extension .EXE), to extract data from which (and often to test and display a list of contents) does not require separate program- everything is done using the SFX archive itself. In other words, you simply pack the information into an SFX archive, and the recipient for whom it is intended only needs to launch this SFX archive (in a similar OS) to receive the unzipped information. Note. In reality, SFX archives are regular archives, to which a small executable module-unarchiver, so if necessary (for example, due to fear that this executable module may be infected with a virus), you can use the appropriate external archiver to work with the SFX archive without running the SFX file itself.
Multi-volume archives
Multi-volume archives are archives consisting of several parts. They are supported in a number of popular archive formats - RAR, ZIP, 7z, etc. To create a multi-volume archive, when packing files, you simply need to select the size of the parts into which the resulting archive will be divided. This function especially convenient when working with files big size(for example, video disk images), since it allows you to save even huge and poorly compressed files on smaller media. Some archivers (for example, RAR) have a function automatic detection the size of each volume depending on the free space on the current media used for archiving, which allows you to make the most efficient use of multi-volume archives, say, for transferring from computer to computer on several flash drives of different sizes.
Continuous Archives
Continuous (English - solid) archiving is a type of archiving in which all files added to the archive are considered by the archiver as one continuous stream of data. Thanks to this approach, it is possible to achieve a significant increase in the compression ratio, especially when packing many files of the same type that are relatively small (with the size of the archiver’s “sliding dictionary”). In addition to the obvious advantage (more powerful compression), continuous archives also have their disadvantages. Since the data in a continuous archive is one continuous stream, in order to extract any file, you first need to unpack all the files that are in the archive before this file, so extracting files located at the end of the archive is slower. Also, operations to change the contents of the archive (adding and deleting files) are performed more slowly than in a regular (non-solid) archive. In addition, if the archive is damaged for some reason, then only files that go before places of damage, and all information after this place will be lost. In other words, continuous archives are good for packaging and storing data that rarely needs to be changed.
Metadata
An archive almost always contains metadata. These include:
- File names (except for some single file compression programs - for example, gzip, where the file name is the name of the archive without extension)
- Identifiers of owners, groups, etc. files and their rights
- File sizes
- Dates of modification, creation and last access to files
- File checksums to verify correct unpacking
- Archive size and checksums
- Redundant data to recover data when damaged
- Digital signature of the archive creator
Nowadays, when popularity World Wide The Web is quite large, the amount of traffic transmitted over Internet networks By FTP protocol nevertheless occupies first place, slightly ahead of the volume of traffic in terms of HTTP protocol. In this light, organizing file archives within the framework of TCP/IP technology is an extremely urgent task.
Archives are used to solve different tasks, however, the most popular on the Internet are free available archives or such archives, access to which is authorized by an anonymous user ID. Thus, these archives can be used as:
Free software collections; collections of programs for beta testing; collections of normative and regulatory documents; and so on.
An FTP archive can also be used as an archive of commercial software that is used in a company, only in this case such an archive should not allow anonymous access to the resources stored in it.
Often, the option of authorized FTP access is also used for messaging, i.e. as a means of communication. This usually happens when the email system does not work for one reason or another.
Currently, the entire system of interaction between FTP exchange components can be represented in the form of a diagram shown in Figure 4.1.
This diagram shows two important technological points: firstly, the archive can be accessed not only from a specialized client program, but also from a universal browser, for example Netscape Communicator or Microsoft Internet Explorer, and secondly, to search for information in FTP archives, you can use the Archie program.
Rice. 4.1. Interaction diagram of FTP exchange components
It should be clearly understood that Archie and FTP are completely different technologies. In most cases, users access the Archie server from the Archie client, which is located on the same machine as the server, i.e. First, the user logs in via Telnet as an Archie user, and then uses a client program (usually launched as a shell) to access the Archie server.
FTP protocol ( File Transfer protocol)
FTP (File Transfer Protocol) is one of the oldest protocols on the Internet and is part of its standards. Data exchange in FTP takes place over a TCP channel. The exchange was built using client-server technology. Figure 4.2 shows the protocol model.
Rice. 4.2. Protocol model
IN FTP connection initiated by the user protocol interpreter. The exchange is controlled via a control channel in the TELNET protocol standard. FTP commands are generated by the user's protocol interpreter and sent to the server. The server's responses are also sent to the user via the control channel. IN general case the user has the opportunity to establish contact with the server's protocol interpreter and by means other than the user's interpreter.
FTP commands define the parameters of the data transfer channel and the transfer process itself. They also determine the nature of work with remote and local file systems.
The control session initializes the data link. When organizing a data transmission channel, the sequence of actions is different, different from organizing a control channel. In this case, the server initiates data exchange in accordance with the parameters agreed upon in the management session.
The data channel is established for the same host as the control channel through which the data channel is configured. The data channel can be used for both receiving and transmitting data.
It is possible that data may be transferred to a third machine. In this case, the user organizes a control channel with two servers and organizes a direct data channel between them. Control commands go through the user, and data directly between servers (Figure 4.3).
The control channel must be open when transferring data between machines. If it is closed, data transmission stops.
Rice. 4.3. Connection with two different servers and transferring data between them
Communication modes
The protocol places great emphasis on in various ways data exchange between machines various architectures. Indeed, there is so much on the Internet, from personal computers and Macs to supercomputers. They all have different word lengths and many different order bits in a word. In addition, different file systems work with different data organization, which is expressed in the concept of access method.
In general, from an FTP point of view, the exchange can be stream or block, with or without encoding in intermediate formats, text or binary. At text exchange all data is converted to ASCII and transmitted over the network in this form. The only exception is IBM mainframe data, which is sent to EBCDIC by default if both communicating machines are IBM. Binary data is transmitted as a sequence of bits or undergoes certain transformations during the control session. Typically, with streaming data transfer, one data file is transferred in one session, and with the block method, several files can be transferred in one session.
Having described in general outline exchange protocol, you can go to the description of exchange tools using the FTP protocol. For almost any platform and operating environment There are both servers and clients. The following describes the standard server and client of Unix-like systems.
Software for accessing FTP archives
To work with Ftp archives you need the following software: server, client and search program. The server provides access to archive resources from anywhere on the network, the client provides user access to any archive on the network, and the search engine provides navigation throughout the entire network of archives.
These Ftp exchange components vary in both form and capabilities across different operating systems, but some general principles In addition, command-line interface-oriented programs remain largely unchanged across different operating environments.
Protocol server - ftpd program
The ftpd command is designed to service requests for information exchange via the FTP protocol. The server usually starts when the computer boots. The syntax for starting the server is as follows:
ftpd [-d] [-1] [-t timeout] d - debugging option; 1 - automatic user identification option; t is the time of passive waiting for user commands.
Each server has its own description of commands, which can be obtained using the help command. Automatic user identification is carried out using the /etc/passwd file. The user password must not be empty.
Exists special file, which contains prohibited users, i.e. those for whom service via the FTP protocol is prohibited. You can enter the archive using an anonymous or ftp user ID. In this case, the server takes measures to restrict access to computer resources for given user. Typically, a special ftp directory is created for such users, in which the bin, etc and pub directories are located. The bin directory contains the commands allowed for use, and the pub directory contains the actual files themselves. The etc directory is not visible to the user and contains user identification files.
File sharing program - ftp
FTP is a user interface for exchanging files using the protocol of the same name. The program establishes a control channel with a remote server and waits for user commands. The remote server ID is specified either as a program argument or in the open interface command.
If the ftp command is running on a user and is waiting for user commands, the "ftp>" prompt is displayed on the screen.
Command syntax:
ftp [-v][-d][-i][-n] v - suppresses server responses and data transfer statistics; n - controls the user identification mode. If this switch is specified, the .netrc file is checked first; i - disables file transfer confirmations when copying files in bulk; d - turns on debugging mode; g - disables name transfer transparency.
Within this course there is no way to list everything ftp commands, so we will focus only on the most necessary ones.
The first such command is open command. This command opens a session with the remote server:
ftp>open polyn.net.kiae.su
After issuing such a command, user identification requests will follow. You can also register a user by user command:
ftp> user anonymous
IN in this example the user does not have special access rights to the remote server and therefore registers as anonymous. In response to the identification request, in this case you should enter your mailing address. Usually it is enough to enter something similar to a postal address to gain access to archive resources, but there are also meticulous servers that check the presence of such an address, so it is better not to deceive anyone and register honestly.
The next most important commands are the cd and ls (dir) commands. The purpose of these commands is quite transparent and understandable to all users - navigation through the file system tree and viewing the contents of directories. Here it is recommended to use the ls command with additional parameters:
In this case, the user can receive a multi-column report indicating file types. However, not all servers work with this combination.
Since two machines are involved in the transfer and reception process, in addition to navigation in the remote file system, navigation in the local file system is also needed. The lcd (local cd) command is used for this purpose. In addition, the user can issue any local shell command if he precedes it with the "!" character:
This command will display the name of the current directory on local machine.
And finally, the most important commands are get, put, mget, mput and bin. The get and put commands can accept or transfer one file:
ftp> get README.TXT
The mget, mput commands are designed to receive/transmit a set of files:
ftp> mget *.gz
The example shows that in the latter case the “*” mask is used. Typically, when transferring groups of files, confirmation is requested for each file. To avoid this, issue the prompt command before sending/receiving. The latter switches the confirmation request mode and when this command is used again, the confirmation request state is restored. Another useful command is the hash command:
The "#" symbol can be replaced with any other one. When working on slow lines or when transmitting large files after turning on the hash mode, the user has the opportunity to see the process of data transfer (the “#” sign is issued after the transfer of each block). The last thing you should pay attention to is the bin command. After issuing this command, by default, data will be transferred in binary data transfer mode. The latter is extremely important, because When transferring to ASCII, programs and archived data cannot be transferred. It is often useful to enable bin mode for character data with an arbitrary line length, such as postscript (*.ps) files, because in ASCII mode there is a limit on line length (usually 254 characters).
To exit ftp, use the quit command.
Search in FTP archives - Archie program
Currently, FTP access is provided from a variety of multiprotocol interfaces (for example, Mosaic or Netscape) or graphical FTP shells such as ftptool for X-Window. All of them are much more convenient and easier to use, but they also consume much more resources.
It is curious that there is an FTP server even for MS-DOS (NCSA Telbin package), not to mention multitasking environments. However, finding the right FTP server on the Internet is a complex and time-consuming task. To make it easier there is special remedy- Archie. Archie was developed at McGill University in Canada. Archie's job is to scan FTP archives to see if they contain the required files. You can work with Archie through a telnet session, through a local client, or via email. To work via telnet, you should open a telnet session and enter the word “archie” in response to login:
telnet archie.mcgill.ca
After the "archie>" prompt appears, you should inquire about the server's capabilities by entering the "help" command.
When working through a local client, simply enter:
archie gnuplot.tar.gz
and in response they receive a list of archives that contain the file “gnuplot.tar.gz”. It should be taken into account that various modifications of clients (especially graphical ones) may differ significantly in syntax from each other.
File archives are a file created using a special program called an archiver, and containing from one to several files and/or directories (folders) in packed form.
Historical aspect
Such archives were used most actively during the use of floppy disks, since file archives make it possible to compress some types of files (excluding graphics and video) in order to place them on a small diskette. With their disappearance, the use of archives mainly moved to the Internet, where they continue to be used mainly in file sharing services and on ftp servers.
Classification of archives
Highlight the following types file archives:
- regular - in one archive file there are several files and/or folders compressed by some method;
- self-extracting - are executable files with the extension .exe; when starting, you only need to specify the unpacking path, the program itself will do the rest;
- multi-volume - includes a number of parts of the archive, which, in addition to their own extension, may have an additional extension indicating the part number: part01...;
- continuous - archives with the highest possible degree of compression, in which all files and folders form a single whole; unpacking one file (folder) is impossible;
- password protected - archives that require a password to be opened.
File archive extensions
Each file has specific extensions. File archives are no exception. These are, first of all, zip, rar, 7z - the most popular extensions used in the operating system Windows system. Such extensions in the GNU/Linux OS can be found very rarely, mainly from those users who have recently switched to using this OS after Windows. Here the most common archives are gz, bz2, xz. Working with these extensions is usually accompanied by tar compression, as a result general expansion looks like tar.gz, tar.bz2, tar.xz. Often tar.bz2 and tar.xz are more efficient in compression than zip. These formats are not common in Windows OS, but can be successfully used there in all common archivers.
The best compression level in the most common Windows OS is 7z, but tests show its slight superiority over other file archive extensions. Working with zip in Windows is available after installing the system, just like in Mac OS X; most GNU/Linux distributions also work with this archive out of the box, since archivers that support most common file archive formats are installed along with the distribution.
Working with file archives
File archives require the presence of special programs that could effectively create and unpack them. It should be noted that most archivers for Windows OS create corresponding items in context menu, which is called by right-clicking. We will look at file archives for desktop computers, but there are also ones for gadgets that can be found in the appropriate stores.
Let's look at the most common file archive programs.
WinZip
By default, it saves files in zip, but you can save in other formats. Using this archiver you can compress mp3 files and jpeg files up to 25% without losing quality. The compression method is selected automatically. There are functions for printing files that are compressed into a given archive, checking them with an antivirus, and others. The latest versions of the application support opening 7z, rar and zipx files.
According to the developers, WinZip provides protection using bank-grade encryption. In addition, the latest versions have the ability to connect to clouds.
In this program, new MS Office document formats can be opened as file archives: docx, xlsx, etc., as well as formats that comply with the international ODF standard.
As the developers say, reducing the size graphic files occurs due to the fact that some formats are replaced by others.
In case of accidental deletion, copying, renaming, files can be restored.
WinRAR
All over the world, zip archives lead in popularity, but Russia goes its own way, and our most popular archiver is WinRAR. This archiver has a command line mode (this is what is used in GNU/Linux environments), the latest versions have also learned to effectively compress media content. It has its own support for a variety of formats, including both the popular rar and zip, as well as the less popular gz, tar, bz2, lzma and others.
In WinRAR you can select the compression time, but it must be taken into account that stronger compression will lead to more time spent on the archiving process. In the settings of this archiver, you can set a low priority, which will increase the loading and unpacking time, but will also reduce the load on the processor, or you can use all processor cores, which will lead to a higher load on them, but will reduce the time of creating an archive or unpacking.
PeaZip
This program is cross-platform and can be installed on many operating systems. Capable of opening more than 180 file archive formats. This is probably a record. It supports simultaneous work with several archives. IN latest versions support for opening zipx, rar, including its fifth version is provided.
This application also supports data encryption, it has the ability to convert a disk into file system NTFS, it is possible to create keys, backup copies files. The program is released for both 32-bit and 64-bit platforms.
7-zip
This archiver creates native 7z formats, although a number of others are supported, including popular formats on Windows and POSIX systems, including GNU/Linux and Mac OS X. Among others, it allows you to open rar, deb archives that contain binary files installers of programs in GNU/Linux OS. According to the developers, the compression rate is 30-70% higher than WinRAR, and 2-10% higher than WinZip.
Unlike the first two archivers, who want users to receive money for using them, the last two belong to open source programs and are free. In 2007, this archiver was recognized as the best by the SourceForge.net project.
Encryption is implemented using the algorithm AES-256 for 7z and zip file archives. Archives packed using the LZMA method are unpacked literally on the fly.
Like PeaZip, there are applications for both 32- and 64-bit platforms.
File archives on the Internet
Many servers in World Wide Web contain them. Internet servers containing file archives are called ftp servers. Until recently, almost everything could be found on these servers - from music to toys and programs for various systems. The fight against piracy in our country has somewhat crippled this segment, and now it mainly houses free products.
FTP servers host GNU/Linux OS repositories, thanks to which each user of these systems has the opportunity to freely install programs signed digital keys, which eliminates the possibility of penetration malicious code to the user’s computer, due to which these systems are famous for their absence of viruses.
Ftp servers can be viewed from any browser; there are special clients for them.
Data exchange from the ftp server with users occurs over a TCP channel. Exchange management is regulated in the TELNET protocol standard.
When using the ftp protocol, it is possible not only to download files to local computer, but also transmit to
Any interested person can create a file archive system using an ftp server.
The server data ensures that file archives are provided and received by both anonymous users and authorized users. Most ftp servers are anonymous.
Despite the described advantages, ftp servers are not without disadvantages. A huge part of the file archives in them are presented without description, and you can only guess what is in front of you through a targeted search.
File transfer can be carried out in text or binary mode. When wrong choice the file may become damaged.
No via ftp servers universal search. There are several solutions, but they are not all universal.
The most common among them is the Archie service. Archie servers are heavily loaded and only work with anonymous ftp. However, the server data is decentralized, the search is carried out using a not entirely clear algorithm, as a result of which, if you go through all the servers (and there are about a dozen of them), you may not find it the information you are looking for. In addition, you must be able to create a search template when using this service.
In addition to using the ftp protocol, the http protocol can be used to access file archives.
File archives represent not only open source software, you can also find various texts, demo versions of proprietary programs and much more.
Finally
Thus, file archives are a necessary thing in order to transmit a large amount of information in a compressed form. This archives can be used locally - on separate computers, and in global network Internet through the use of special ftp and http servers. The most common programs for creating archives and unpacking them are WinRAR, WinZip, PeaZip, 7-zip. The last two programs are free and can be used for free. Most archivers support all the most common archive formats.
File FTP archives
The FTP (File Transfer Protocol) service is used to access Internet file archives.
More precisely, it allows you to establish a connection with one of the computers on the Internet (via FTP, using ftp program on your local machine), view the files available on it and copy the necessary ones to yourself.
File Transfer Protocol (FTP) is a protocol that allows you to easily transfer files and documents. It is usually considered as one of the methods of working with remote networks.
File Transfer Protocol (FTP) is the most common protocol for transferring files between computers. It allows you to work with any type of file.
Like many other types of services, FTP works on the principle of a client-server architecture system. Therefore, to work with FTP you usually need special programs– FTP clients. The servers in this case are FTP servers located somewhere on the network and providing access to the file archives they serve.
One of the most common types of FTP servers is anonymous FTP server. When working with them, you do not need to know the username and password to connect to the server and receive files. An anonymous FTP server typically uses "anonymous" or "ftp" as the username and your email address as the password.
In FTP archives on their servers, almost everything large manufacturers hardware post drivers for their devices, which can be “downloaded” by the owners of these devices.
Although FTP is great for transferring files, good funds It doesn't have the ability to work with files scattered across many computers. In this regard, it was developed improved file transfer system. It is called Gopher.
Using a menu system, Gopher not only allows you to browse lists of resources, but also forwards required material, and it is not at all necessary to know where it is located. Gopher is one of the most comprehensive browsing systems available, integrated with other programs such as FTP or Telnet. It is widespread on the Internet.
Gopher computers are linked into a single search engine called Gopherspace. Access to Gopher spaces is carried out through the menus they offer, and search is carried out using several types of search engines. The most famous among them are the Veronica system and the index search system of the global information server (wAIS - wide Area Information Server).
Teleconferences
The teleconferencing system emerged as a means for groups of people with similar interests to communicate. Since its inception, it has spread widely, becoming one of the most popular services Internet.
This type of service is similar to Internet mailing lists, except that messages are not sent to all subscribers of a given newsgroup, but are posted on special computers, called teleconference servers or news servers. Subscribers to the teleconference can then read the incoming message and, if desired, respond to it.
A teleconference is like a bulletin board where everyone can post their own announcement and read the announcements posted by others. To make it easier to work with this system, all teleconferences are divided into topics, the names of which are reflected in their names. On this moment there are about 10,000 different newsgroups discussing everything you can imagine.
To work with the teleconference system, you need special software with which you can establish a connection to the news server and gain access to the teleconference articles stored on it. Since the news server stores articles very large number newsgroups, users usually select those that are of interest to them (or, in other words, subscribe to them), and then work only with them.
After subscribing to the selected newsgroups, you will have to establish a connection to the news server to view incoming messages. The difference is that you can configure the newsgroup reader to only track the status of the newsgroups you've signed up for, rather than forcing you to view the entire list.
Essentially, Telnet is a protocol that allows you to use the computing resources of a remote computer. In addition, this is usually the name of a program that allows you to access the resources of a remote computer using this protocol. Often these concepts are combined into one and, when we're talking about about Telnet, we mean the telnet program that works using the TELNET protocol.
Telnet allows you to work with remote computers in text terminal mode. Thus, you type commands and see the results of their execution on your screen, but in fact all the commands are executed on the computer with which you have established a connection. Only the information that you enter from the keyboard and that is displayed on your screen is transmitted over the network. This creates the impression that you are working only with your own computer.
To use Telnet, you need access rights to the computer you want to work with. In most cases, this means that you must know the appropriate username and password. Another option would be that you are personally logged in as a user on this computer.
Telnet is one of the fundamental types of Internet service. It provides the user with the opportunity to contact his computer, even while hundreds of kilometers away, view his mail, check the progress of running tasks and, if necessary, launch new ones, chat with friends who are currently working on the computer, and much, much more other.
The main condition is to connect your computer to the Internet and be able to terminal access. (An example of this would be computers running the UNIX operating system.)
>>Informatics: File archives
File archives
File archive servers.
Hundreds of thousands of Internet servers are file archive servers, storing hundreds of millions of files. File servers supported by many development companies software and manufacturers of computer hardware components and peripheral devices. The software hosted on such servers is freely distributed (freeware) or shareware, and therefore, by downloading a particular file, the user does not violate the law on copyright for software. Lately music archive servers that store albums and musical compositions popular performers in MP3 format.
File transfer protocols.
Access to files on file archive servers is possible both via HTTP and a special transfer protocol FTP files(File Transfer Protocol). The FTP protocol allows you not only to download files from remote file archive servers to a local computer, but also vice versa, transfer files (Upload) from a local computer to a remote Web server, for example, in the process of publishing a Web site. For example, to download the file file.exe stored in the pub folder from the file archive server ftp.server.com, you must specify the URL of this file. When specifying a file URL, the FTP protocol is written as follows: ftp://
As a result, the universal resource locator takes the form: ftp://ftp.server.com/pub/file.exe It consists of three parts:
ftp:// - access protocol;
ftp.server.com - Domain name file archive server;
/pub/file.exe - file path and file name.
For the convenience of users, many file archive servers (freeware.ru, www.freesoft.ru, www.download.ru, etc.) have a Web interface, which allows you to work with them using browsers. are integrated systems for working with various information resources Internet and therefore include file download managers. After activating the link to the file in the window that opens, you need to specify the folder on the local computer in which the file should be saved. The file download will begin, the process of which is displayed on the information panel (transfer speed, volume of downloaded and remaining parts of the file, etc.).
Specialized managers download files.
However, it is more convenient to use specialized file download managers (for example, FlashGet) to work with file archives. Such managers allow you to increase download speed by splitting files into parts and simultaneous download all parts. In addition, they allow you to continue downloading a file after the connection to the server is broken, contain a file search tool for other file archive servers, allow archive files in the process of downloading them, etc. The user is provided in numerical and graphically detailed information about the file download process (current and average download speed, download completion percentage, estimated download time, etc.). Specialized file download managers are integrated into browsers and when you activate a link to a file in the browser window, they begin the process of downloading it using the download manager.
FTP clients.
FTP servers are servers with which files can be exchanged using the FTP protocol. FTP servers, according to their functional purpose, can be both file archive servers and Web servers on which Web sites are hosted. From file archive servers, files are downloaded (Download) to the local computer, and vice versa, files are transferred (Upload) from the local computer to Web servers in the process of publishing Web sites. File exchange (downloading and transferring) with file archive servers and Web servers is carried out using specialized programs- FTP clients (for example, the FTP client is part of the file Total manager Commander). Access to file archive servers to download files to your local computer is usually anonymous and does not require a username and password. On the contrary, access to WEB servers for the purpose of transferring files to remote server During the process of publishing a Web site, it requires user identification, i.e., entering a username and password. The FTP client includes a Site Manager, which allows you to create a list of servers with which you plan to work. Presents the local and remote computers, ensures that the file continues to download after the connection is lost, etc. During the file transfer process, the necessary information is displayed: the percentage of the transferred file volume, the transfer speed, the remaining time, etc.
Off-line browsers.
For fast loading Web sites for the purpose of further leisurely browsing in offline mode special programs are used - off-line browsers. Off-line browsers (for example, Offline Explorer) allow you to download entire Web sites or individual parts of a site to your local computer. The user can set the required “depth” of loading a Web site (the number of subdirectories), downloading multimedia files associated with pages, downloading Web pages from other Web servers via hyperlinks, etc. It is possible to continue loading the site after disconnecting and updating previously downloaded sites.
Computer Science and ICT: Textbook for 10th grade. N.D. Ugrinovich
