Asymmetric archiver. Archiving programs

Creation of archives;

Extracting files from archives;

Adding files to the existing archive;

Creation of self-extracting archives;

Creation of distributed archives on low-capacity media;

Testing the integrity of the archive structure;

Full or partial recovery of damaged archives;

Protection of archives from viewing and unauthorized modification.

Self-extracting archives are used when there may be no means to extract files from the archive. A self-extracting archive is prepared on the basis of a regular archive by attaching a small program module to it. The archive itself receives the .exe extension, which is typical for executable files. To extract files from the archive, the user simply launches the file for execution, after which the files are automatically extracted from the archive.

Distributed archives (also called multivolume archives) are created in cases when it is planned to create a large archive on low-capacity media (for example, on floppy disks). In this case, the archive is split into fragments and written to media.

WinZip performs partitioning directly to floppy disks. WinRAR and WinArj allow you to pre-split the archive into fragments of a given size on the hard disk, then they can be transferred to external media.

When creating a distributed archive, WinZip creates archive fragments on floppy disks with the same name, so each disk should be marked with labels on a sticker. If necessary, you can find out the archive volume number by the label on the disk (My computer, CM for disk A :, Properties, General tab - in the Volume label field, you can find out the volume number of the distributed archive).

Archivers WinRAR, WinArj mark all files of the distributed archive with different names.

In most cases, archives are protected with a password. It should be noted that passwords based on the characters of the English alphabet and numbers are removed very quickly by brute force methods (used when cracking a password). Therefore, it is recommended to use the Russian alphabet and punctuation marks along with the English alphabet.

One of the most popular Windows archivers is WinRAR.

ZIP archivers are the standard today.

· Antivirus software provide the user with the necessary means to combat the previously mentioned computer viruses.

System programs are developed, configured and maintained in working order by specialists, who are usually called system programmers. They must be highly qualified, know in detail the hardware of the computer and how to work with data at the machine level. An ordinary user has to constantly deal with system programs, but from the point of view of their operation, the use of their capabilities to solve their problems. We will get acquainted with some programs of this group in the following chapters of the manual.

Such programs can also be classified as utilities. By definition E.V. Kaspersky, “a computer virus is a program that can create copies of itself (not necessarily exactly the same as the original) and inject them into files, computer system areas, computer networks, etc. At the same time, the copies retain the ability to further distribute. "

The virus can distort the text of the program, as a result of which it becomes completely inoperable.

A virus can "infect" a program; such a program is capable of transmitting a virus to other programs and computers, i.e. to infect them, just like a patient infected with, for example, the flu, has the ability to transmit his virus to others.

Mostly program files such as COM, EXE are infected. Text files i.e. files containing texts of programs in the programming language, texts of documents, etc. they do not get infected with a virus, they can only be distorted. And also there may be others such as Word and Excel,

Infection with PC viruses often leads to the failure of a large number of expensive software packages, which can result in high material costs. Fighting viruses is often very time consuming. Antivirus programs are created to effectively combat numerous viruses. Here is some of them:

· doctor programs"Cure" programs, restoring their original appearance and removing the virus from them;

· filter programs intercept the calls of viruses to the operating system, used for propagation and harm, and report them to the user.

The most famous Russian antivirus programs include Kaspersky Anti-Virus(http: //www,kav.ru) and Dr.Web(http://www.drweb.ru). These programs confidently pass all tests without exception and provide a reliable level of protection.

In recent years, simple antiviruses have gradually disappeared from the scene, giving way to "combined" programs, which include both antivirus and a firewall that protects against network worms and Trojans. In addition, a modern antivirus must be able to neutralize spyware and adware modules - although they do not belong to viruses, the harm from them is also quite tangible.

The best in functionality and reliability among similar "combines" are the latest versions Kaspersky Anti-Virus and Symantec (Norton) Antivirus. The program also demonstrates good results Panda titanium from Panda Software and kit ZoneAlarm Security Suite... The cost of all these packages is quite high.

There are also free antivirus programs - for example, AVG Antivirus(http://www.grisoft.com) and avast(http://www.avast.com). The capabilities of these programs are somewhat faster.

However, they are able to protect against really dangerous viruses, moreover, these programs practically do not "slow down" the computer.

Finally, there are free antivirus "scanners". If full-fledged antiviruses "hang" in RAM all the time and scan an open file or a running program in the "shadow" mode, then the scanners simply check the entire contents of the hard disk. However, it is impossible to update the anti-virus database of such scanners in automatic mode - it is "hardcoded" in the body of the programs, but new versions of the scanners themselves appear quite often. Perhaps the best program in this class is Dr.Web Cure.IT! (http://drweb.ru/download/).

The performance of computers and the size of RAM and hard drive are constantly increasing. However, the amount of data that needs to be stored grows much faster. Until recently, it seemed that a 2-3 dozen gigabyte disk would reliably solve the problem of insufficient disk space. However, there are new programs that are very demanding on hardware resources. The sizes of multimedia files, which I would also like to save, exceed all reasonable limits. As a result, it turns out that the hard disk is full and the user is faced with the task of freeing it up at least a little.

Initially, they take an inventory of the contents of the hard drive and try to sort all the data into the necessary and those that can be deleted. However, there are files that are not needed at the moment, and you don't get a hand to delete them. These can be old projects, photographs, toys, a selection of your favorite pieces of music, or a collection of distributions of frequently used programs and utilities. It is advisable to pack them as compactly as possible and put them in a "back corner" until requested. In this case, they will take up much less space on your hard disk and at the same time will always be at hand, and if you wish, you will always have the opportunity to restore the original copy.

You can pack (compress) data on a hard disk using a special program - an archiver. There are many varieties of these programs. They differ in compression algorithm, speed of operation, set of additional functions, user interface, etc.

In addition, you may need an archiver if you actively exchange information electronically with other people. By writing a large text document and compressing it with an archiver, you can send it by email much faster. The compressed document is much smaller than the original, sometimes ten or more times smaller, so it takes less time to transfer. The recipient will be able to restore the original text using the same program as you, by doing the opposite.

Information compression algorithms are being actively improved, and modern archivers allow you to compress data much more efficiently. However, the most advanced, in terms of information compression, programs are not always the most multifunctional, and therefore the most widespread. Therefore, most users opt for programs that provide a lower compression ratio, but have a well-designed interface and a large number of additional features.

What archivers are available today, by what parameters they compete with each other, where to find a fresh archiver - this is not a complete list of issues that are covered in this article. In addition to theoretical questions, we will consider 10 popular archivers.

Briefly about information compression

Compression of information is a problem that has a fairly long history, which ran parallel to the history of the development of the problem of encoding and encrypting information. All compression algorithms operate on the input stream of information in order to obtain a more compact output stream using some transformation. The main technical characteristics of compression processes and the results of their work are:

compression ratio - the ratio of the volumes of the initial and resulting streams;
compression rate - the time spent on compressing a certain amount of information in the input stream until an equivalent output stream is obtained from it;
compression quality - a value that shows how strongly the output stream is packed when it is re-compressed using the same or a different algorithm.

There are several different approaches to the problem of information compression. Some have a very complex theoretical mathematical base, others are based on the properties of the information flow and are algorithmically quite simple. Any data compression or compression algorithm is designed to reduce the volume of the output information stream in bits by means of its reversible or irreversible transformation. Therefore, according to the criterion associated primarily with the nature or format of the data, all compression methods can be divided into two categories: reversible and irreversible compression.

By irreversible compression is meant such a transformation of the input data, in which it is impossible to obtain an exact copy of the original data from the archive, but only a copy that is more or less close to the original can be obtained. Some of the information that was in the original is irretrievably lost. Such approaches and algorithms are used to compress, for example, data from raster graphic files. This approach uses the property of the structure of the graphic file format and the ability to present a graphic image that is approximately similar in display quality (for perception by the human eye) in several ways. Therefore, in addition to the degree or amount of compression in such algorithms, the concept of quality arises. And since the original image changes during the compression process, the quality is characterized by the degree of correspondence between the original and the resulting image. For graphic files, such a correspondence is determined visually, although, of course, corresponding intelligent algorithms and programs have been developed for this. This approach is implemented in popular formats for presenting video and photo information, known as JPEG and JFIF algorithms and JPG and JIF file formats. Irreversible compression cannot be applied in those areas where accurate recovery of compressed information is required.

Reversible compression means such a transformation of the input data, in which an exact copy of the input information can be obtained from the archive using a restoring or decompression algorithm.

Reversible data compression is based on a simple idea: mapping the representation of data from one group of characters to another, more compact series of characters. Consider two algorithms: Huffman coding and LZW coding (based on the initial letters of the surnames Lempel and Ziv - its creators and Welch, who significantly modified it).

Understanding how each algorithm works provides a foundation for understanding compression in general. Both algorithms are lossless compression algorithms and are suitable for compressing any type of data.

Huffman coding, first proposed sometime in the early 50s, reduces the number of bits used to represent common symbols and increases the number of bits used for rare symbols. The LZW method, on the other hand, encodes character strings using an input stream to build an extended alphabet based on the strings it processes. Both approaches work by reducing unnecessary information in the input.

Huffman coding

Huffman coding is perhaps the most well-known data compression method. It is based on the premise that some symbols are used more frequently in data representation than others. Indeed, the most common representation - the ASCII alphabet - uses 8 bits for each character. At the same time, it is known that, for example, in English the letter "e" will clearly occur more often than the letter "q", although we use the same number of bits to represent them. By using only 4 bits for "e" and 12 bits for "q", multiple bits can be won.

Huffman coding formalizes the idea of relating the length of a character to the probability of occurrence of characters. Static Huffman coding requires a probability table before you start compressing data. This table can be taken from the results of statistical studies (such tables have been published for some data, for example for the English language), or the compression system can scan the input data to determine the probabilities of characters before starting to compress the data.

The need for a probability table for each type of data being compressed is the biggest challenge when using Huffman codes. This won't be a problem if you know you will always compress English text. In the general case, when you do not know the probability of characters for your input data, the use of static Huffman codes is impractical.

Fortunately, the dynamic version of Huffman compression can change the encoding scheme depending on the nature of the changes in the input stream.

LZW encoding

The LZW algorithm, first introduced by Welch in 1984, has become a widely used method in the past few years. The CompuServe GIF file format uses LZW compression; ARC, compress from UNIX, Stuffit and PkZip do this too. The algorithm itself is patented by Sperry.

Despite some complexity, this method is quite powerful and fast, which, in fact, determined its popularity. LZW works by expanding the alphabet — it uses complementary characters to represent strings of ordinary characters. To use LZW compression to 8-bit ASCII codes, you expand the alphabet using nine or more bit codes. The additional 256 characters provided by the 9-bit code are used to store strings of 8-bit codes, which are determined from the strings in the input stream.

The compressor maintains a string table consisting of strings and their corresponding codes. The string table corresponds to the extended alphabet. The compressor starts with a table of strings defined with only 256 letter codes. If you are using 9-bit codes, the string table has 256 additional blanks; if you are using 10-bit codes it has 768 empty elements, etc.

The compression algorithm works like this. Start at line zero. Read the symbol and add it to the line. If the row is already in the table, keep reading until you get a row that is not in the table. Add this line to your table of strings. Write the code for the last known line that matches the output. Use the last character as a basis for a new line and keep reading until you've exhausted all input.

Which archiver to choose?

Which archiver is better? The answer to this question is far from straightforward. If you look at the table in which the archivers "compete" (you can do this on the site http://arctest.narod.ru), you can see that the number of programs taking part in the "competition" exceeds a hundred. How to choose the required archiver from this variety?

Choosing an archiver, you need to be guided by its versatility and reliability, of course, not forgetting about the main parameters - quality and compression speed. Among the archivers used today, many are specific to certain file formats, which, undoubtedly, should be used, but for the intended purpose. General analysis shows that you should not choose an archiver that provides maximum data compression. A gain in compression (by 7-10%) usually leads to a significant increase in the processing time of the original data, which can differ hundreds of times even on very powerful personal computers.

If you need an archiver, as they say, "for all occasions", then you can evaluate how good this program is by referring to the test, in which programs that process different types of files compete. You can view the list of archivers and the results of their testing in the "Testing" section of this article. More detailed information on the characteristics and test results of more than 100 different archivers can be found on the website http://arctest.narod.ru.

However, it should be noted that only quantitative parameters are analyzed in the tests, such as compression speed, compression ratio and some others, while there are a number of parameters that determine the usability of archivers. Let's list some of them.

Support for various formats
While most programs support one or two formats, some of them, such as the WinAce program, support many formats and, in particular, perform compression in ACE, ZIP, LHA, MS-CAB, JAVA JAR and decompression formats. in ACE, ZIP, LHA, MS-CAB, RAR, ARC, ARJ, GZip, TAR, ZOO, JAR formats.
Ability to create solid archives
Solid archiving is archiving in which the increase in compression increases when there are a large number of short files being processed at the same time. Some archivers, for example ACB, always create solid-archives, others, such as RAR or 777, provide the ability to create them, and some, for example ARJ, do not know how to do this at all.
Ability to create multivolume archives
Multivolume archives are necessary when files are transferred from computer to computer using floppy disks and when the archive does not fit on one floppy disk.
Ability to work as an archive manager
Various programs are more or less capable of keeping track of the archives on your disk. Some archivers, such as WinZip, allow you to quickly get to any archive file (and its contents), no matter where it is on the disk.
Password protection capabilities
In principle, archiving is a kind of encryption, and if decoding is available using a password, then this, of course, can be used as a means of restricting access to confidential information.
Ease of use
Not the least factor is usability - a well-thought-out menu, mouse support, an optimal set of options, a command line, etc. It should be noted that for many (especially non-professionals) the habit factor is important. If you are used to working with a certain program and you are told that there is an alternative program that wins your ten points on some test, this may well mean that the winning program compresses files 2% better, which may be for you it does not matter. Moreover, it is likely that this program is less convenient to use, etc. On the other hand, if you are missing 2% to compress the program you are distributing to the size of a floppy disk, then such a program is a godsend for you.
Creating self-extracting archives
Some programs allow creating archives with * .exe extension. In this case, you just need to run the file for execution, and the archive will automatically open, even if you do not have the required archiver at hand.
Automatic deletion of files after archiving
By setting this option, you do not have to delete the source code manually after archiving. The program will do it for you.
Placement in the archive of author's comments
When creating an archive, it is useful to add comments to it with a brief description of the contents.

Let's consider the most interesting standard archiver programs for today.

A short description of 10 popular archivers

1. ACB

Version v2.00c

Supported Platform: DOS

Status: shareware

The name of the archiver comes from the Associative Coder of Buyanovsky.

The program came out about three years ago and during this time remains one of the leaders in terms of compression ratio.

The ACB v.2.00c version was developed as a means of preliminary compression of information for subsequent sending over the network. ACB algorithms provide a high compression ratio, but the program does not have the function of adding or extracting individual files from the archive. There is only an option to unpack the entire archive. Files of type hidden, system, read_only are also placed in the archive. The maximum size of an individual file should not exceed 64 MB, and the maximum number of files in an archive should not exceed 4096.

The size of the string (PATH (s) \ NAME (s) .EXT (s) \ ATTRIBUTE (s)) must not exceed 256 KB. Recommended hardware requirements - Pentium 133, 16 MB.

Install

2. ACE

Version v2.04

Supported platforms: DOS, OS / 2, Win

Status: shareware

The program has a wide range of options, a friendly user interface, and a well-developed documentation system. A variety of languages are supported (English, German, Dutch, etc.).

ACE supports long filenames, functions for creating self-extracting (SFX) and multivolume archives, encryption, commenting, authentication. Implemented specialized algorithms for compressing images, sound, executable files, etc., the maximum size of the dictionary is 4 MB. Implemented protection and recovery of failed archives, switching the interface language (including Russian), setting associations (file types with external programs), a separate unpacking utility, external support for ARJ, RAR and ZIP.

The algorithms used provide a high compression ratio at a high speed (in terms of compression ratio, the archiver is close to RAR, while it usually wins in speed).

Install

4. JAR

Version v1.02 (1999)

Supported platforms: DOS, Win9x, WinNT

Status: shareware

JAR is currently considered one of the best archivers in terms of reducing the size of the archived file. According to the author's data, JAR outperforms such popular archivers as PKZIP 2.04, UC2 rev 3, RAR 1.55, RAR 2 and LHA in terms of compression.

JAR uses technology other than solid to get high compression ratio, fast updates and extract from archive.

The program can simultaneously archive up to 50,000 files.

Provides the ability to support multivolume archives, built-in support for recovering files from damaged archives and integrity check to limit hacker or virus intrusions. The function of "protected" archives is available, which blocks any attempts to modify the file. It is also possible to use a password to prevent unauthorized access.

There is an option to convert long filenames to short ones when unzipping files in DOS. The program allows you to overcome the DOS barrier (640 K) by using EMS and / or XMS.

Install

5. WinRAR

Version 2.90 Final

Supported platforms: Windows, Linux, BeOS and DOS-32

WinRAR is a 32-bit version of the RAR archiver for Windows. Besides full RAR and ZIP support, WinRAR 2.90 can unpack UUE, GZ, TAR, ARJ, LZH, ACE, CAB, BZIP2, JAR (Java ARchive) and ACE 2.0 archives. WinRAR has an original compression algorithm with high compression ratios, especially on executable files, large text files, etc. The number of compressed files included in the archive is not limited.

There is support for ZIP archives; graphical interactive interface along with command line.

WinRAR provides the ability to create solid archives, which gives you the benefit of archiving a large number of files.

It is possible to create self-extracting (SFX), regular and multivolume archives.

Available locking, encryption, file order list, volume labels.

There are also additional functions, such as encryption, adding archived comments, logging errors, etc.

Install

6. WinZip

Version v8.1 (2001)

Supported platforms: Win9x, WinNT, Mac

Status: shareware

One of the most popular programs on the Internet. The ZIP algorithm itself is freely used in dozens, if not hundreds of programs, and yet WinZIP is the standard program for working with archives for most Windows users. WinZip is easy to use, has long name support and is optimized for Windows 95/98 / NT.

WinZIP can view and extract files from other less common archive formats such as ARJ, LZH, ARC, TAR, TAZ, TGZ, Z, GZ, CAB, UUE, XXE, UU, B64, HQX, BHX. There are functions for installing programs, screen themes and screen savers from archives, performing many operations through step-by-step Wizards, compressing and sending files by mail, checking the contents of archives with an external antivirus, managing bookmarks of selected archive directories, the ability to integrate with Windows Explorer is supported (adding commands in the context menus) There are separate utilities for working from the command line, integration with popular Internet browsers, and creating self-extracting archives.

A convenient system of hints allows you to quickly master the program.

The drag-and-drop interface is fully supported.

WinZip has a very convenient auto-install feature for software distributed as Zip files.

For easy archiving / unzipping of files, WinZip offers the WinZip Wizard. While this feature may be annoying for sophisticated users, it can come in handy for beginners.

It is possible to organize files into "favorite" folders (Favorite Zip Folders). WinZip allows you to organize Zip files into a single “sheet”, which makes it easier to combine and sort Zip files no matter where they are physically stored. The search function allows you to find any Zip files "lost" on your disk. It is possible to create self-extracting files. WinZip can be configured to work with most modern antivirus scanners.

Install

7. WaveZip

Version 2.0(May 2000)

Supported platforms: Win9x, WinNT, Mac

Status: shareware

The program was developed as a tool for compressing large audio WAV files that take up a lot of space.

WaveZIP is easy to use and allows you to quickly find, select and convert files. Drag-and-drop functionality from Windows Explorer is supported.

The program implements a special MUSICompress technology from Soundspace Audio. The compression is absolutely lossless, the algorithms are optimized specifically for the compression tasks of the WAV format (the average compression ratio, depending on the file type, reaches 30-60%).

Install

8. WavPack

Version 3.92(October 2001)

Supported platforms: Win9x, WinNT, Mac

Status: free

Console compressor specialized in audio compression. Provides lossless packing / decompression of 16/24-bit mono and stereo WAV files. WavPack is fast, with 25-50% compression for pop music and slightly better compression for classical music and high dynamic range compositions. The maximum attainable packing level is 87% (for periods of silence). A configurable lossy compression mode is provided (up to 67% with inaudible loss and up to 77% with noticeable noise), compression of "raw" audio files of unknown formats is possible, fast packing mode is supported, there is a WinAMP plugin for playing compressed WavPack files.

Install

9. PowerArchiver

Version v7.02(July 2001)

Supported platforms: Win9x, WinNT

Status: shareware

Powerful multi-format Windows GUI shell that allows (mainly by its own means) to work with archives in ZIP, RAR, CAB, ARJ, LHA, ACE, ARC, TAR, BZIP2, TAR.BZ2, GZ, BH, ZOO, XXE, UUE formats ... In addition to standard operations, PowerArchiver can rename files in archives, install programs from them, scan content for viruses, convert archives from one format to another, protect them with a password, repair, create multivolume and self-extracting (SFX) archives. The program also allows you to view TXT, RTF, BMP, ICO, GIF, WMF, EMF and JPG files by its own means, print lists of archive files or export them in TXT and HTML formats. There are tools for managing the list of quick access to frequently used directories, changing the appearance of the keypad using skins, performing data backup operations using scripts, searching for program updates on the Internet, creating a separate archive for each compressed file.

PowerArchiver has a user-friendly Office 2000-style switchable interface with detailed help system and integrates with Windows Explorer, providing support for Drag & Drop operations and convenient context menus.

Install

10. ZipMagic

Version 4.0 (2001)

Supported platforms: Win9x, WinNT

Distributed as Trial version

Not so long ago (a year or two ago) Mijenix released an updated version of its popular ZipMagic program. For those who do not know what this program is, let me explain: ZipMagic (formerly ZipFolders) is a Windows 95 / NT program designed to simplify and speed up working with ZIP archives. The purpose of the program is to provide the ability to work with archives as with ordinary disk folders. That is, all zip files on disks magically "turn" into regular directories. At the same time, neither Explorer, nor Norton Commander, nor any other program suspects that they are dealing with archives. You can work with pseudo-folders as usual: rename them, run and install programs, games from them, view, edit, copy, rename files, create and delete subdirectories, etc. ZipMagic will perform compression / decompression operations unnoticed by you, and significantly faster than most of the well-known zip packers.

For example, when viewing a document from a zip folder, the program will unzip it and substitute the original unnoticed for you and for the OS, and when you save the changes made to the document, it will automatically repack the file without losing the modified data. In addition, ZipMagic, like all common archivers, allows you to perform standard operations on archives: converting, encrypting, testing / patching, adding / editing archive comments, converting archives to self-extracting EXE archives, etc. The program allows you to automatically split archives into floppy disks, even if you create a self-extracting EXE archive.

Interest in ZipMagic is the method of notifying about the finding of a bad archive: when you enter a bad zip folder, you may unexpectedly find a text file in it, warning about found errors.

The new version of the program adds support for most of the new archive formats and encodings. Among them: RC, ARJ, CAB, GZ, LHA / LZH, RAR, TAR, ZOO, UU / XXEncode and many others. At the same time, to work with files of these formats, you do not need the utilities that created them themselves. To work with them, the ZipTools utility supplied with ZipMagic is intended. All of the aforementioned file types are automatically associated in the registry with this utility and, of course, are opened with it.

ZipTools is a kind of Explorer, with which you can perform all the standard functions inherent in file managers (copying, transferring, renaming files, Drag & Drop support, customizing panels, sorting, multiple windows, etc.), as well as specific functions such as UU -encoding, converting to ZIP, formatting disks, searching for files / computers and the like. In this case, the program can be configured to emulate the hotkeys of Norton Commander, Explorer or Xtree Gold. In addition, ZipTools allows you to quickly view more than 60 file / document formats, including multimedia, without leaving the program (this is done both using the QuickView tools supplied with Windows 95, and using your own tools).

ZipMagic also comes with the ZipWizard utility, an automated tool for creating / converting / unpacking archives for beginners, providing a step-by-step simplified interface for performing standard operations.

In addition, the program comes with special zip-plugins for browsers and e-mail. The first - ZipSurfer - is designed to work in Netscape Navigator, Netscape Communicator and Internet Explorer and allows you to unpack, view archives freshly downloaded from the Internet, install programs from them and perform other operations with archives without leaving your browser (something similar is available in the well-known WinZip) ...

The second plug-in - ZipMail - is an add-on to programs such as Eudora Light, Eudora Pro, Microsoft Exchange, Outlook 97 and Outlook 98. It allows you to automatically compress files sent by mail as attachments.

There are a wide variety of options that can be changed in ZipMagic options, including Windows NT-specific options. You can define the program autorun options, set the compression ratio with which files will be compressed when creating an archive-folder, set the program cache size, hotkeys, select disks for which ZipMagic functions will work, define the time to enable / disable program functions. You can also define which applications will still treat zip archives as files rather than directories, such as backup and disk utilities. In addition, you can enable options for showing the program button in the window titles (next to the minimize button) and determine which items to add to the right-click file context menu. This context menu will change depending on the file type. For zip archives / folders, you will see standard archive commands, and for regular files, you will see compression commands and a “Send To with compression” drop-down menu that works the same as the standard Windows “Send” menu, only the files / folders you have selected will be in front of packed with it. The program can be configured both through the interface, using the ZipMagic icon in the System Tray area (about hours), and through the special "command line" utility ZMCmdLn.

ComputerPress 2 "2002

A distinction should be made between the archiving program itself, the format of the archives and the compression methods. Even the same compression method can be implemented in different ways. For example, there are over a dozen archiving programs that can create ZIP archives. In turn, data in ZIP format can be compressed using various methods: Deflate, Deflate64, BZip2. The Deflate method has several implementations with different speeds and compression ratios. With this method, the 7-zip archiver allows you to create archives in ZIP and 7Z format.

Usually archivers can create archives in their own exclusive format using their original methods. For example, the RAR archiver allows you to create RAR archives. The archive format and compression methods are the main advantages of this or that archiver.

In the simplest case, the archiver only allows you to pack or unpack one file. In addition to the actual data compression, modern archivers provide some additional functions. There are several main ones:

Compression of some files and entire directories;

Creation of self-extracting (SFX) archives. That is, you do not need an archiver program to unpack the archive;

Changing the contents of the archive;

Encryption of the contents of the archive;

Information for recovering an archive in case of partial damage and the ability to recover damaged archives;

Splitting the archive into several parts or volumes;

Console version of the program for working from the command line;

Graphical (GUI) version of the program.

It is worth noting that, despite the formal presence, the implementation of each additional function can be performed at a completely different level.

In addition to differences in functionality, archivers can be divided into two groups: asymmetric and symmetric. Asymmetric archivers require significantly less time and memory for the decompression operation than for the packing operation. This allows you to quickly retrieve the contents of the archive on low-power computers. Symmetric archivers require the same amount of RAM and time for packing and unpacking operations. The use of such archivers on a wide range of computers or for online access to the contents of the archive is limited. The well-known RAR archiver uses the asymmetric dictionary compression method as the main one, and for texts it can use the symmetric PPM method. Thus, unpacking RAR archives compressed with the maximum compression ratio may not be possible on computers with limited RAM. All or nearly all of the advanced high compression ratio archivers are symmetric.

Despite the very modest data on the prevalence of archivers, there are many of them. Most of them belong to the category of experimental and archivers with limited functionality. However, each of them allows you to perform the actual data compression procedure.

Supported platforms: Windows, Linux, BeOS and DOS-32

WinRAR is a RAR and ZIP file archiver for 32-bit and 64-bit Windows and Pocket PC operating systems. It is considered one of the best archivers in terms of the ratio of the compression ratio to the speed of work. Distributed under a shareware license. The Pocket PC version is licensed Freeware.

Possibilities:

Creation of archives in RAR and ZIP formats.
Unpacking CAB, ARJ, LZH, TAR, GZ, ACE, UUE, BZIP2, JAR, ISO, 7z, Z files.
The ability to encrypt archives using the AES (Advanced Encryption Standard) algorithm with a key length of 128 bits, while the password hash using the SHA-1 algorithm is used as the encryption key.
Ability to work with files up to 8.589 billion (approximately 8 x 109) gigabytes.
Creation of self-extracting, continuous and multivolume archives.
Adding additional information to the archives for restoring the archive in case of its damage, including the creation of special recovery volumes, allowing you to restore a multivolume archive if parts with information are damaged.
Full support for NTFS file system and Unicode file names.
Command line support.

· Since version 2.90, support for a new archive format - RAR3 is introduced. Previous versions cannot handle the new format;

· Starting with version 3.50, themes and skins are supported, as well as correct embedding into the context menu on x64 Windows systems;

· Since version 3.60, the compression algorithm supports multi-core processors and processors with Hyper-threading technologies - this provides a significant increase in the compression speed;

· Since version 3.70 the archiver is officially compatible with Windows Vista, creates SFX-archives with a request for privileges;

· Since version 3.80, ZIP archives are now supported that contain Unicode filenames in UTF-8 format;

· Since version 3.90 there is a division into 32- and 64-bit versions of the program. The 64-bit version works only on 64-bit Windows OS and provides some performance boost.

· Since version 4.00, the RAR archiving algorithm has been changed, which significantly increases the decompression speed. Depending on the type of data, the decompression speed can be up to 30% faster. A password manager appears, which allows you to save passwords for archives for future use.

WinZip is a shareware file archiver and compressor for Microsoft Windows and Apple Mac OS X by Corel. PKZIP is the main format, although other archive formats are supported.

Possibilities:

Create, add, extract from ZIP archives as well as native .zipx format
Support for compression algorithms JPEG, LZMA (12.0), bzip2 (9.0), PPMd (10.0) and special algorithms for audio files (based on WavPack), which allows you to reduce the archive due to the potential increase in compression and extraction times (especially when using PPMd).
Decompression of .bz2, .rar, .iso, .img, 7-zip files
Built-in support for LHA archives (.lha and .lzh)
Customizable integration into the Microsoft Windows shell.
Supports 128- and 256-bit AES encryption keys. This replaced the less secure PKZIP 2.0 encryption method used in earlier versions. Version 9 also provides support for 64-bit encryption in PKZIP.
Direct burning of archives to CD / DVD
Backup automation
FTP protocol support
Sending ZIP archives by email
Unicode support (since 11.2)

The ZIP archiver (PKZIP) was originally created for MS-DOS in 1989 by PKWare.

WinZip was created in early 1990 as a commercial graphical interface for PKZIP. Around 1996, the creators of WinZip included compression code from the PKZIP project, thus obviating the need for a console version.

From version 6.0 to version 9.0, registered users could download the latest software versions using the original registration information and thus receive updates for free. Since version 10.0 the free update system has been disabled. WinZip is available in standard and professional versions.

In May 2006, Corel Corporation, known for its WordPerfect and CorelDRAW product lines, announced that it had completed its acquisition of WinZip Computing.

Prior to version 11.2, it was possible to enable it using external archive support programs ARC, ARJ.

Since version 14.5 the menu of the program's graphical shell has been changed to the Ribbon interface.

April 2011 - Version 15 was released, which supports the Russian language.

2012 - WinZip ver. 16.5, the engine of which is optimized for multi-core processors. Also added support for OpenCL for AMD GPUs (however, not for Intel and Nvidia), while the performance gain in this application for Trinity and Llano APUs was up to 45%.

7-Zip is a free, highly compressed file archiver. Supports multiple compression algorithms and multiple data formats, including 7z proprietary format with highly efficient LZMA compression algorithm. The program has been developed since 1999 and is free, and also has open source code, most of which is freely distributed under the terms of the GNU LGPL license, with the exception of the unRAR decompressor code, which has limitations. The main platform is Windows (including Windows CE), where two versions of the program are available: a graphical interface and a command line version. The console version has been ported by the community of developers for POSIX systems under the general name p7zip. Ported versions for other systems, like the original 7-zip program, are available on the SourceForge site (as of November 7, 2010, the program has been downloaded over 109 million times). 7-Zip is the 2007 SourceForge.net Community Choice Awards winner in Best Design and Best Technical Design.

Possibilities

Supported algorithms:
LZMA, LZMA2, PPMd, Bzip2, Deflate and Deflate64
Supported formats:
packing and unpacking: 7z, BZIP2 (BZ2, TB2, TBZ, TBZ2), GZIP (GZ, TGZ), TAR, ZIP, XZ;
unboxing only: 001, ACE, ARJ, CAB, CHM, CPIO, DEB, DMG, FLV, ISO, JAR, LHA, LZH, LZMA, LZO (TZO), MSI, NSIS, PE, RAR, RPM, SWF, SWM, VHD, WIM, XAR, Z (TAZ); FAT, HFS, MBR, NTFS, UDF, SquashFS, CramFS
Very high compression ratio in the new 7z format thanks to the use of the advanced Lempel-Ziv algorithm.
For ZIP and GZIP formats, the compression ratio is 2-10% higher than that of PKZIP and WinZip.
The ability to create self-extracting archives for the 7z format.
In 7z format, it is possible to create multivolume archives (with the exception of self-extracting).
AES-256 encryption for 7z and ZIP archives.
Integration into Microsoft Windows and Windows NT shell.
Plugin for the FAR Manager program.
Plugin for Total Commander and Unreal Commander (wcx) programs.
Built-in performance testing utility.
Multilingual GUI (Windows only) with dual window file manager functionality.
Powerful command line version.
Special edition for 64-bit Windows operating systems.
Support for Unicode encoding for file names.

7-Zip uses multithreading and allows you to use for compression, depending on the algorithm or format, a different number of threads. When creating archives in which files can be compressed independently of each other (for example, ZIP), the program can use up to 8 streams simultaneously. For the LZMA compression algorithm, the archiver can simultaneously use up to 2 streams. The impossibility of using more of them is due to the sequential nature of continuous compression. The LZMA2 compression algorithm does not have this disadvantage.

When compressing in the 7z format, special normalizing filters are also used. So, for more optimal compression of 32-bit x86 code, normalizing converters BCJ and BCJ2 are used. The program also has an optimizing delta converter for some types of media such as uncompressed 24-bit images.

Compression results are highly dependent on the data being compressed. Usually 7-Zip compresses to 7z format 4-25% better than zip format.

7-Zip 4.65 takes 24th place in the rating of archivers in terms of compression ratio, for comparison, the popular WinRAR 3.80 and WinZip 12 take 32nd and 34th places, respectively. The leaders of the PAQ rating are better known for their GUI modifications KGB and WinRK have an order of magnitude longer compression times.

Dignity

free open source software distributed under the GNU LGPL free license (except for the unRAR unpacker, the license of which prohibits the restoration of the RAR compression algorithm); As a consequence, support for multiple platforms.
open archive format and compression algorithm.
high compression ratio. In general, you can choose the parameters at which the file size and compression speed will be similar to WinRAR.
high unpacking speed (for archives with the LZMA compression method). According to the author:
decompression speed reaches 20-30 megabytes per second on a 2 GHz Intel Core 2 or AMD Athlon 64 processor.
unpacking speed is about 1-2 megabytes per second when using processors ARM, MIPS, PowerPC and the like at a frequency of 200 MHz.
multithreaded compression. If on a single-core processor the speed of 7-Zip is close to WinRAR, then on a dual-core 7-Zip it is much faster;
support for AES-256 encryption;
support for 64-bit systems;
the program has many precise settings for compression algorithms; for inexperienced users there are ready-made presets;
the total size of files in one 7z archive can be 16 exabytes;
There is an open 7-Zip API that allows you to integrate 7-zip with other software products.

disadvantages

Does not save information about file permissions.
Prevents files from being extracted if all parts of the archive are not available.

conclusions

Data compression is widely used. Almost everywhere, one might say. For example, PDF documents tend to contain concise information. Quite a few EXE executable files are compressed with special packers. All kinds of multimedia files (GIF, JPG, MP3, MPG) are kind of archives.

The main disadvantage of archives is the impossibility of direct access to data. They must first be extracted from the archive or unpacked. The unpacking operation, however, like packing, requires some system resources. This is not an instant operation. Therefore, archives are mainly used with relatively rarely used data. For example, to store backups or installation files.

So, when choosing an archiver, you should not be guided only by the speed of work and the provided compression ratio. It is necessary that it has a developed and convenient windowed interface, supports different platforms (so that there are no compatibility problems) and has a large number of additional features. It is important to take into account the prevalence and possible further support by the authors of new versions when choosing an archiver.

Bibliography

1. Zverev V.S. Informatics: A textbook for university students. Astrakhan, 2003

2.http: //wikipedia.ru

3. Povalyaev. E. "Archivers". ComputerPress No. 2 2007

4. Volovnik A. "Meet Information Technologies". SPb. BHV-Petersburg. 2006

5. Sennov A. "The course of practical work on the PC" SPb. BHV-Petersburg. 2005

A regular file contains encoded data. In order for the data to occupy a smaller amount of memory, various algorithms for packing (compressing) information are used, which reduce the volume by eliminating the redundancy of the codes. For example, the repetition information of the character sequence can be written in different ways.

The purpose of archiving programs is to create archive files in order to reduce their volume. The amount of data is an important parameter for storing information, transferring it to external media or sending it over the network.

The archiver allows you to unpack archives received by the user from different sources.

Rice. 1. Window of the archiver WinRar

The archiver makes it possible to split the archive, the volume of which exceeds the volume of the storage medium, into volumes and place them on several media.

One archive file can contain one or more packed files. Archiving multiple general purpose files and storing them in one archive file is very convenient for sending by e-mail, storing, deleting files after their expiration date. Besides, you can add other files to the existing archive (fig. 1). For example, several files contain reports for each month of the year. They can be stored in one zip file and a new file added monthly. It is easy to search for such files.

2.2.2. Archiving options

The archive file has a name specified either by the user or by the default archiver. It stores packed data, as well as service information about such properties of archived files as their names before archiving, extensions, dates and times of their creation, size before creating the archive, and information about properties of the archive file.

An important parameter is the size of the file to be packed before archiving and the size of the file in the archive after archiving, as it makes it possible to assess the need for data compression. For example, if you archive graphic files with the JPEG or GIF extension, then, evaluating the size of the file before and after compression, you can see that the archiving of such a file did not significantly change the size. Files with these extensions are already packaged.

2.2. 3. Types of archives

The archiver allows you to create various types of archives: an archive from a group of files or from a single file, a multivolume archive, a continuous archive, archives of different formats (rar, zip, sfx).

Multivolume archive Is a single archive file stored on multiple media. The Split archive into volumes with specified size option is needed when the archive is a file that is larger than the external media. In this case, splitting into volumes will allow you to place it on different media, and later - to collect it into one file. If the size of the archive file does not exceed the size of the media, then dividing it into volumes does not make sense.

Continuous archive Is a RAR archive, packed in a special way, in which all compressed files are treated as one sequential data stream. Continuous archiving is supported only in the RAR format, this kind of archive does not exist for the ZIP format.

Continuous archiving significantly increases the compression ratio, especially when adding a significant number of small files with similar content to the archive. However, keep in mind that continuous archiving has some disadvantages:

updating continuous archives (i.e. adding files to an existing archive or deleting them) is slower than regular archives;
To extract a single file from a continuous archive, you have to analyze all the previously zipped files, so extracting individual files from the middle of a continuous archive is slower than extracting from a regular archive. However, if all or several of the first files are extracted from a continuous archive, then the unpacking speed is practically equal to the unpacking speed of a regular archive;
if any file in the continuous archive is damaged, the files following it will not be able to be extracted. Therefore, when saving a continuous archive to an unreliable medium (for example, a floppy disk), it is recommended to add recovery information.

Continuous archives are created when:

the archive is supposed to be updated rarely;
the archive is supposed to be unpacked completely, and not to extract one or several files from it;
a tighter compression ratio needs to be achieved despite the fact that the packing speed will be slow.

Self-extracting archive Is the zipped file to which the executable is attached. It allows you to extract files by simply double-clicking the archive. Such an archive is called an SFX archive (SFX is an abbreviation of the English name Self eXtracting, which translates as self-extracting).

The type of the archive file is exe (application), that is, an executable file. It unpacks files on its own without any additional programs. It is convenient to use when it is not known whether the required archiver is available on the computer.

The WinRar archiver works with SFX archives in the same way as with any other. Such an archive is slightly larger than usual in size.

To create an SFX archive, it is enough to select the Create (SFX) archive checkbox in the archive parameters window.

Files created by different archivers have extensions that indicate the name of the archiving program, for example, WinZip archives have the zip extension, Winrar - rar. The Winrar archiver allows creating archives of both zip and rar types.

ZIP archives are widespread. For example, a large number of archives on the Internet are in zip format. Zip archives are faster than rar archives.

The RAR format provides better compression than zip in most cases, especially when creating continuous archives. Another important RAR feature is support for multivolume archives. In addition, the RAR format has some very important features that zip lacks. For example, adding recovery information that allows you to recover a physically damaged file.

The RAR format allows you to process files of almost unlimited size, while the size of a single file in a ZIP archive cannot exceed 2 GB.

In the window for specifying archive parameters (Fig. 2), there are switches that can be used to select the type of archive. The user can choose various methods of information compression.

Rice. 2. Window for setting archive parameters

The user can check the box next to that option (Fig. 2), which will set the execution of the actions he needs.

2.2.4. Extracting files from an archive

Extract (unpack) - reverse archiving process. During the unpacking dialog, you need to select a folder and parameters for the files to be extracted from the archive. To do this, the required folder is indicated in the folder tree in the extraction window (Fig. 3).

Rice. 3. Window for extracting files from archive

By default, the folder gets the same name as the archive (without the extension) and is located in the current folder. In the Path for extraction field, enter the required path (if the required folder does not exist, it will be created) or select the folder in the folder tree panel.

During extraction, you can set some additional parameters:

Update mode.
Extract and replace files (default action).
All selected files are extracted.
Extract and update files. This option allows you to extract only those from the selected files that are not in the destination folder or whose copies in the archive have a later creation date than the files on the disk.
Update existing files only. This extracts only those of the selected files that are in the destination folder, but their copies in the archive have a later creation date than the files on the disk. Files that are not on disk are not extracted.

Introduction

1. Methods of compressing computer files

2. Programs archivers

Conclusion

List of sources used

Introduction

The performance of computers and the size of RAM and hard drive are constantly increasing. However, the amount of data that needs to be stored grows much faster. Until recently, it seemed that a 300-500 gigabyte disk would reliably solve the problem of insufficient disk space. However, there are new programs that are very demanding on hardware resources. The sizes of the multimedia files that I would like to save exceed all reasonable limits. As a result, it turns out that the hard disk is full and the user is faced with the task of freeing it up at least a little.

Initially, they take an inventory of the contents of the hard drive and try to sort all the data into the necessary and those that can be deleted. However, there are files that are not needed at the moment, and you don't get a hand to delete them. These can be old projects, photographs, toys, a selection of your favorite pieces of music, or a collection of distributions of frequently used programs and utilities. It is advisable to pack them as compactly as possible and put them in a folder on demand. In this case, they will take up much less space on your hard disk and at the same time will always be at hand, and if you wish, you will always have the opportunity to restore the original copy.

You can compress data on a hard disk using a special program - an archiver. Archivers are programs for creating archives. Archives are designed to store data in a convenient compact form. The data is usually files and folders. Typically, the data is pre-compressed or packaged. Therefore, almost every archiver is also a data compression program. On the other hand, any data compression program can be considered an archiver. Compression efficiency is the most important characteristic of archivers. The size of the created archives depends on it. The smaller the archive, the less space is required to store it. The transmission requires less bandwidth of the transmission channel or takes less time. The advantages of archives are obvious when you consider that the data is reduced in size by half and five times.

In addition, the archiver may be needed if the user actively exchanges information in electronic form with other people. By writing a large text document, compressing it with an archiver, you can send it by e-mail much faster. The compressed document is much smaller than the original, sometimes ten or more times smaller, so it takes less time to transfer. The recipient will be able to restore the original text using the program, making the reverse operation.

Today, there are many varieties of such programs. They differ in compression algorithm, speed of operation, set of additional functions, user interface, etc. However, the principles of information compression are built on the same principles.

1. Methods of compressing computer files

A large number of various methods, their modifications and subspecies for data compression have been developed. Modern archivers, as a rule, use several methods at the same time. There are some basic ones.

1) Run-length encoding (RLE stands for run-length encoding)

A very simple technique in which a sequential series of identical data items is replaced by two characters: the item and the number of times it is repeated. Both an additional and an intermediate method are widely used. As an independent method, it is used, for example, in the graphic BMP format.

2) Vocabulary method (LZ - short for Lempel Ziv - names of authors)

The most common method. A dictionary consisting of sequences of data or words is used. When compressed, these words are replaced with their codes from the dictionary. In the most common implementation, the original data block itself acts as the dictionary.

The main parameter of the dictionary method is the size of the dictionary. The larger the vocabulary, the more efficient. However, for heterogeneous data, an excessively large size can be harmful, since when the data type changes abruptly, the dictionary will be filled with irrelevant words. This compression method requires additional memory to work effectively. Approximately an order of magnitude more than needed for the original data of the dictionary. An essential advantage of the dictionary method is the simple and fast unpacking procedure. No additional memory is required. This feature is especially important if you need quick access to data.

3) Entropy method (Huffman - Huffman coding, Arithmetic coding - arithmetic coding)

In this method, the more common data items are encoded when compressed with a shorter code, and the rarer data items are encoded with a longer code. Due to the fact that there are much more short codes, the total size is smaller than the original one. It is widely used as a complementary method. As an independent method, it is used, for example, in the graphic JPG format.

4) Method of context modeling (CM - short for context modeling - context modeling)

This method builds a source data model. When compressing the next data element, this model gives out its prediction or probability. According to this probability, the data item is entropy encoded. The more closely the model matches the original data, the more accurate it will make predictions, and the shorter the data items will be encoded.

A lot of memory is required to build an efficient model. When unpacking, you have to build exactly the same model. Therefore, the speed and RAM requirements for packing and unpacking are almost the same. At the moment, context modeling methods provide the best compression ratio, but are extremely slow.

5) PPM (PPM - Prediction by Partial Matching)

This is a special kind of contextual modeling. The prediction is made based on a certain number of previous data items. The main parameter is the order of the model, which sets this number of elements. The higher the order of the model, the higher the compression ratio, but more RAM is required to store the model data. If the RAM is not enough, then such a model with a large order shows low results. PPM is especially effective for compressing text data.

6) Pre-transforms or filtering

These methods are used not for compression, but for presenting information in a form convenient for further compression. For example, uncompressed multimedia data is characterized by smooth changes in signal level. Therefore, a delta transformation is used for them, when a relative value is taken instead of an absolute value. There are filters for text, executables, databases and others.

7) Method of sorting the data block (BWT - short for Burrows Wheeler Transform - by the name of the authors)

This is a special kind or group of transformations based on sorting. Almost any data can be subjected to this transformation. Sorting is performed on blocks, so the data is pre-divided into parts. The main parameter is the size of the block to be sorted. To unpack the data, you need to do almost the same steps as for packing. Therefore, the speed and RAM requirements are almost the same. Archivers that use this method usually show a high speed and compression ratio for text data.

8) Continuous blocks or continuous mode (Solid mode - continuous mode)

In many compression methods, the initial portion of the data or file is poorly encoded. For example, in a dictionary method, the dictionary is empty. In the contextual modeling method, the model is not built. When the number of files is large and their size is small, the overall compression ratio is significantly degraded by these initial sections. To prevent this from happening when moving to the next file, the information obtained from the previous files is used. A similar effect can be achieved by simply presenting the source files as a single contiguous file.

This method is used in many archivers and has a significant drawback. To unpack an arbitrary file, you must also unpack the files that appear at the beginning of the archive. This is necessary for the correct filling of the vocabulary or the construction of the model. There is also an intermediate option when continuous blocks of a fixed size are used. Compression losses are minimal, but to extract a single file, which is located at the end of a large archive, you need to unpack only one contiguous block, and not the entire archive.

9) Segmentation

In all compression methods, when the data type is changed, the transition itself is very poorly coded. The dictionary becomes irrelevant, the model is tuned to different data. In these cases, sharding is applied. This is a preliminary breakdown into homogeneous parts. These parts are then encoded individually or in groups.

I would like to emphasize that there are a large number of compression methods. Each method is usually focused on one kind or group of real data. The complex use of the methods shows good results.

2. Programs archivers

computer file compression archive

Compression of some files and entire directories;

Creation of self-extracting (SFX) archives. That is, you do not need an archiver program to unpack the archive;

Changing the contents of the archive;

Encryption of the contents of the archive;

Information for recovering an archive in case of partial damage and the ability to recover damaged archives;

Splitting the archive into several parts or volumes;

Console version of the program for working from the command line;

Graphical (GUI) version of the program.

It is worth noting that, despite the formal presence, the implementation of each additional function can be performed at a completely different level.

Ramotrim the most popular archiving programs:

1. WinRAR

Version 2.90 Final

Supported platforms: Windows, Linux, BeOS and DOS-32

There is support for ZIP archives; graphical interactive interface along with command line. WinRAR provides the ability to create solid archives, which gives you the benefit of archiving a large number of files.

It is possible to create self-extracting (SFX), regular and multivolume archives. Available locking, encryption, file order list, volume labels.

There are also additional functions, such as encryption, adding archived comments, logging errors, etc.

2. WinZip

Version v8.1

One of the most popular programs on the Internet. The ZIP algorithm itself is freely used in dozens, if not hundreds of programs, and, nevertheless, for most Windows users, it is WinZIP that serves as the standard program for working with archives. WinZip is easy to use, has long name support, and is optimized for Windows environments.

WinZip has a very convenient auto-install feature for software distributed as Zip files.

For easy archiving / unzipping of files, WinZip offers the WinZip Wizard. It is possible to organize files into "favorite" folders (Favorite Zip Folders). WinZip allows you to organize Zip files into a single “sheet”, which makes it easier to combine and sort Zip files no matter where they are physically stored. The search function allows you to find any Zip files "lost" on your hard drive. It is possible to create self-extracting files. WinZip can be configured to work with most modern antivirus scanners.

3. WaveZip

Version 2.0

The program was developed as a tool for compressing large audio WAV files that take up a lot of space.

WaveZIP is easy to use and allows you to quickly find, select and convert files. Drag-and-drop functionality from Windows Explorer is supported.

4. WavPack

Version 3.92

Supported platforms: Win9x, WinNT, Mac

5. PowerArchiver

Version v7.02

Supported platforms: Win9x, WinNT

Powerful multi-format Windows GUI shell that allows you to work with archives in ZIP, RAR, CAB, ARJ, LHA, ACE, ARC, TAR, BZIP2, TAR.BZ2, GZ, BH, ZOO, XXE, UUE formats. In addition to standard operations, PowerArchiver can rename files in archives, install programs from them, scan content for viruses, convert archives from one format to another, protect them with a password, repair, create multivolume and self-extracting (SFX) archives. The program also allows you to view TXT, RTF, BMP, ICO, GIF, WMF, EMF and JPG files by its own means, print lists of archive files or export them in TXT and HTML formats. There are tools for managing the list of quick access to frequently used directories, changing the appearance of the keypad using skins, performing data backup operations using scripts, searching for program updates on the Internet, creating a separate archive for each compressed file.

6. ZipMagic

Version 4.0

Supported platforms: Win9x, WinNT

Mijenix has released an updated version of its popular ZipMagic software. The purpose of the program is to provide the ability to work with archives as with ordinary disk folders. That is, all zip files on disks magically "turn" into regular directories. At the same time, neither Explorer, nor Norton Commander, nor any other program suspects that they are dealing with archives. The user can work with pseudo-folders: rename them, run and install programs, games from them, view, edit, copy, rename files, create and delete subdirectories, etc. ZipMagic will quietly perform compression / decompression operations, and significantly faster than most known zip packers.

ZipMagic also includes the ZipWizard utility, an automated tool for creating / converting / unpacking archives for beginners, providing a step-by-step simplified interface for performing standard operations.

The second plugin, ZipMail, is an add-on to programs such as Eudora Light, Eudora Pro, Microsoft Exchange, Outlook 97, and Outlook 98.

The advantages and disadvantages of the described programs can be represented in the form of graphical drawings.

Conclusion

List of sources used

1.http: www.compression.ru.

2.http: www.maximumcompression.com

3. Povalyaev. E. "Archivers". ComputerPress No. 2 2007

4. Volovnik A. "Meet Information Technologies". SPb. BHV-Petersburg. 2006

5. Sennov A. "The course of practical work on the PC" SPb. BHV-Petersburg. 2005

Asymmetric archiver. Archiving programs

Briefly about information compression

Huffman coding

LZW encoding

Which archiver to choose?

A short description of 10 popular archivers

1. ACB

2. ACE

4. JAR

5. WinRAR

6. WinZip

7. WaveZip

8. WavPack

9. PowerArchiver

10. ZipMagic

2.2.2. Archiving options

2.2. 3. Types of archives

2.2.4. Extracting files from an archive

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