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Archiving programs Archive file MS DOS PKZIP and ARJ RAR archivers Windows WinRAR 2.5 archivers WinRAR features WinZip 7.0 Comparative test of performance and compression ratio of the most popular archivers (WINRAR, WINZIP, RAR).
Archiving programs and their characteristics

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On the menu
Archiving programs
Created by various developers special programs to archive files. Some of them are distributed free of charge, some - on a commercial basis (for a fee), but most programs of this kind are distributed as "Shareware". those. they can be obtained free of charge, but if you want to use them permanently, you must send the specified (usually small, up to $50) reward to the authors or distributors. As a rule, programs for archiving files allow you to put copies of files on disk in compressed form into an archive file, extract files from an archive, view the contents of an archive, and so on. Different programs differ in the format of archive files, speed of work, the degree of compression of files when placed in an archive, and ease of use. The most common archiving programs have approximately the same capabilities and none of them is superior to others in all respects: some programs work faster, others provide a better degree of file compression. Even if we compare programs only in terms of compression ratio, there is no leader among them: different files compress better different programs. The principle of operation of archivers is based on the search for "redundant" information in a file and its subsequent encoding in order to obtain a minimum volume. The most well-known method of archiving files is to compress sequences of identical characters. For example, inside your file are sequences of bytes that are frequently repeated. Instead of storing each byte, the number of repeated characters and their position is fixed. For example, a file to be archived is 15 bytes long and consists of the following characters: B B B B B L L L L L A A A A A

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IN hexadecimal system 42 42 42 42 42 4C 4C 4C 4C 4C 41 41 41 41 41 The archiver can present this file in following form(hexadecimal): 01 05 42 06 05 4C 0A 05 41 This means: from the first position, the character "B" is repeated five times, from position 6, the character "L" is repeated five times, and from position 11, the character "A" is repeated five times. To store a file in this form, only 9 bytes are required, which is 6 bytes less than the original one. The described method is simple and very effective way file compression. However, it does not provide much space savings if the text being processed contains no a large number of sequences of repeated characters. A more sophisticated method of data compression, used in one form or another by almost any archiver, is the so-called optimal prefix code and, in particular, encoding with variable length characters (Huffman algorithm). A variable length code allows the most frequently occurring characters and groups of characters to be written in just a few bits, while rare characters and phrases will be written in longer bit strings. For example, in any English text the letter E is more common than Z, and X and Q are among the least common. Thus, using a special lookup table, it is possible to encode each letter E with fewer bits and use a longer code for rarer letters.
On the menu

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Popular archivers ARJ, PAK, PKZIP work on the basis of the Lempel-Ziv algorithm. These archivers are classified as adaptive dictionary encoders, in which text strings are replaced with pointers to identical strings that occur earlier in the text. For example, all the words in a book can be represented as page numbers and line numbers in a dictionary. The most important feature of this algorithm is the use grammar parsing the previous text with its arrangement into phrases that are recorded in the dictionary. Pointers allow you to link to any phrase in a fixed size window preceding the current phrase. If a match is found, the current phrase is replaced by a pointer to its previous counterpart. When archiving, as well as when compressing, the degree of compression of files is highly dependent on the file format. Graphic files such as TIFF and GIF are already pre-compressed (although there is a variant of the TIFF format without compression) and here even the best archiver will find little to pack. A completely different picture is observed when archiving text files, *.BMP files and the like. All programs for archiving can be conditionally divided into two categories: For command line MS-DOS (ARJ, PKZIP, RAR, etc.) For WINDOWS OS (WINZIP, WINRAR, etc.)
On the menu

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archive file
An archive file is a set of one or more files compressed into a single file, from which they can be extracted in their original form if necessary. The archive file contains a table of contents that allows you to find out which files are contained in the archive. The following information is stored in the archive's table of contents for each file it contains: file name; information about the directory that contains the file; date and time of the last modification of the file; file size on disk and in the archive; a loopback code for each file used to check the integrity of the archive; You can determine with which program a particular archive file was archived using the extension. For example: game.rar - archived using the RAR archiver. game.arj - archived using the ARJ archiver. game.zip - archived using a ZIP archiver. The question involuntarily arises why there are so many archivers and all for one purpose only - to compress the file size. Different programs differ in the format of archive files, speed of work, the degree of compression of files when placed in an archive, and ease of use.
On the menu

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MS DOS archivers
With the development of the computer, the amount of information stored in it began to increase, which in turn led to the development of technologies for storing this information in a compressed form, that is, in archives. To do this, a lot of programs were invented for archiving information. However, when working with this information, it is sometimes undesirable to open the full archive in order to take one or two required files, or simply to see what kind of information is in the archive. Archiving programs, with the exception of a few, do not provide convenient shells that allow you to easily, quickly and visually deal with the contents of archives. The most famous archiving programs for MS-DOS: ARJ (developer - Robert K. Jung), PKZIP (PKWARE Inc.), IHA (Haruyasu Yoshizaki), ZOO (Rahul Dhesi). The undisputed leader in the world over the past 5 years has become the RAR archiver. Currently, RAR is actively replacing ZIP as the main utility for compressing FTP archives in INTERNET networks. RAR is the only worldwide used program created by a Russian programmer (with the exception of TETRIS). All archivers differ in the compression algorithms used, archive file formats, speed, etc.
On the menu

Slide 7

PKZIP and ARJ
PKZIP Works from the command line. Various functions for maintaining zip archives are performed by different programs: pkzip - placing files in an archive pkunzip - extracting files from an archive zip2exe - creating a self-extracting archive pkzipfix - repairing a damaged archive. View help for working with the pkzip archiver using the following commands: pkzip /h pkunzip /h zip2exe /h ARJ Works from the command line. Performs all functions for maintaining .arj archives, incl. support for multi-volume archives. Arj has a very large number of keys. You can automate many actions - creating backup disk, archiving starting from some date, appending to the archive name current date(arh970821.arj), archiving a file from a specific location, multiple levels of compression, and so on. In version 2.55 it is possible to work with long names. Advantages: a very large number of keys, which makes it possible to automate a large number of functions. Protection of the archive from damage. Disadvantages: the lack of an interactive mode, some inconvenience in the presence of some key in environment variable(ARJ_SW) and the launch line - mutual destruction.
On the menu

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RAR
1. Introduction The RAR archiver was created as a fairly versatile tool for compressing files containing the most various information, which combines the advantages and conveniences of programs of two classes of a command line archiver and a full-screen shell for viewing and other manipulations with archives. In some cases, the use of RAR cannot be replaced by any of the existing archivers, and the logical and simple interface makes it a convenient tool for working with archives. In terms of its technical characteristics, RAR is not inferior to widespread and popular archivers, and in some respects it surpasses them. 2. Specifications 2.1. Compression ratio On files like .EXE, .COM, .LIB, .OBJ, .OVR and similar RAR, as a rule, provides the maximum compression ratio compared to other archivers, surpassing them by about 0.5 - 3% On individual files (large .LIB , some others) the gain can reach 5-7% of the packaged size. The compression method usually does not significantly affect the result. Text Information compressed approximately at the level of other archivers (depending on the type of text and compression method) on files up to 32 kilobytes in size. on large text RAR files generally outperforms most other archivers. When packing database files, the compression method (m0 - m5) can significantly affect the size and operation time. Compression ratio graphic information strongly depends on the kind of files. When creating a continuous (solid) archive containing many small files of the same type, the compression ratio is 10 - 40% or more higher than that achieved when packing into a regular archive
On the menu

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2.2. Additional features In addition to the standard functions, RAR provides a full-screen interface: selection of files to be packed and unpacked; emulation of the structure of subdirectories in the archive; work with the "mouse"; saving parameters in a configuration file; viewing packed and regular files in text or hexadecimal form. Special functions: splitting the archive into parts (volumes) for transferring to floppy disks; creation and modification of self-extracting archives (SFX); creation of self-extracting archive volumes (SFX); creation of continuous (solid) archives with a high degree of compression; protection of information by passwords; protection of archives from modification; saving information about the archive author; restoring the structure of damaged archives; adding comments to the entire archive and to individual files; native support for ANSI escape sequences in the comments. Work with ZIP archives, ARJ, LZH in full-screen mode: selection of files to be packed and unpacked emulation of the structure of subdirectories in an archive performing basic operations on archives
On the menu

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On the menu
3.Working with RAR from the command line 3.1. Call format: rar - - There can be only one command, any number of keys. The list file may contain the names of the files to be processed, separated by a carriage return or a space. A file with a comment may contain a comment that is added to the archive when it is created, but not when it is modified. The decompression path, used together with the "e" and "x" commands, indicates the subdirectory where the decompressed files will be placed. If this subdirectory does not exist, it will be created. 3.2. Description of commands a: adds the specified files to the archive m: transfers the specified files and subdirectories to the archive. Upon successful completion of packing, all specified files and subdirectories are removed from the disk. Removal of subdirectories will be performed only if the -ed switch was not used, and *.* or the name of the subdirectory was specified as the name of the added files. mf: transfers the specified files to the archive. If the package is successfully completed, all specified files are removed from the disk. d: removes the specified files from the archive: extracts the specified files from the archive, restoring the subdirectory structure (if the -r switch was specified during archiving). e: extracts the specified files from the archive into the current subdirectory v: view the contents of the archive. Issued full path access to the file and its name, file comment, uncompressed and packed size, degree of packing, date and time of the last modification of the file, its attributes, checksum, compression method and the minimum RAR version required for decompression. If you need to view all archive volumes (volumes), then the name of the archive is replaced with *.

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IN Windows system there are no built-in functions for working with packed archives, so most users have to acquire special utilities and at the same time solve the problem of the diversity of archival formats. Capacity of magnetic disks and random access memory is constantly growing, data transmission channels are becoming more powerful, and yet the amount of information transmitted and stored is still a very significant factor that forces us to use software to work with packed data.
On the menu
WINDOWS archivers

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The WinRAR utility, developed by Russian programmer Evgeny Roshal, allows you to work with ZIP archives, but the main format for it is RAR (also developed by Roshal). In addition, it is possible to create self-extracting EXE archives, as well as use external programs for unpacking and viewing archives such as ARJ, LZH and CAB. The program creates multi-volume archives only in RAR format.
On the menu
WinRAR 2.5

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The RAR format outperforms ZIP, ARJ, and LZH in terms of compression efficiency, but the greatest advantage of this technology is in the case of "continuous" archives, which do not allow changes and are processed quite slowly. The WinRAR distribution kit is an EXE file of about 650 KB, after installation the package takes up almost 1.5 MB. There are versions of the archiver in English and Russian. The archiver window resembles the My Computer system utility, archives look and behave like ordinary folders. You can replenish archives and extract objects from them using drag and drop. To view packed files, the program has a built-in visualization module, but you can also connect an external viewing utility. The program is equipped with a very comprehensive help system. E. Roshal's utility is compact, convenient, quite versatile, its price is not as attractive as that of WinZip, but less than that of other leaders in this review - ZIP Explorer Pro and Zip Magic, so WinRAR may be the best choice for many. WinRAR is the 32-bit version of the popular RAR archiver for Windows, a powerful archive creation and management tool.
On the menu

Slide 14

WinRAR features:
full support RAR archives and ZIP; original highly efficient data compression algorithm; special multimedia compression algorithm; shell with support for drag & drop technology; command line interface; management of archives of other formats (CAB, ARJ, LZH, TAR, GZ, ACE, UUE); support for solid archives, in which the compression ratio can be 10 - 50% higher than with conventional compression methods, especially when packing a significant number of small similar files; support for multi-volume archives; creation of self-extracting (SFX) regular and multi-volume archives using standard or additional modules SFX; recovery of physically damaged archives; other additional functions such as encryption, adding archive comments (supporting ANSI ESC sequences), error logging, etc.
On the menu

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WinZip 7.0
Introduction. A shareware utility developed by Nico Mak Computing is probably the most famous backup program for Windows. The EXE file with the WinZip distribution takes about 940 KB; after installation, the volume of the program files is 2 MB. The program has built-in tools for manipulating archives and packed files in ZIP, TAR, GZIP and CAB formats, and also allows you to connect external modules for working with ARJ-, ARC- and LZH-files. All operations with archives can be performed using drag and drop, long names objects (including Cyrillic ones) are processed normally.
On the menu

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Working with the program Let's start with the most common scenario of working with the WinZip program. Let's say the directory XXXX contains files X1, X2, ..., Xn. They must be packed into a single archive. Find the folder XXXX, select the files X1, X2, ..., Xn (using the left mouse button and the Ctrl or Shift buttons). Then, after right-clicking with the mouse, select the Add to Zip command.
On the menu

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Compressing Word documents (doc or rtf) into an archive gives a very significant savings in disk space (up to 95%). A somewhat more modest result is achieved when compressing html files (up to 80%). Harder with graphic files, bmp can be compressed up to 99%, but when archiving tif, jpg, gif, the savings will be up to 35, 25, 10%, respectively. However, when sending files by e-mail, it is necessary to take into account not only their physical size, but also their number, because it also takes time to process a request to send each file "attached" to a letter. The fact that so many recipients of your correspondence use all kinds of anti-virus programs and / or firewalls that can easily ignore any doc file because of its "suspiciousness" also speaks in favor of closing files with zip before sending them by e-mail, and the zip file is likely to slip through.
On the menu
When specifying the name of the archive file, the zip extension can be omitted, it is enough to enter only the name (in our case, "x") and click the Add button. The result is the appearance of the x.zip file in the XXXX folder (you could have specified another location)..

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Working interface
Through File, you can create a new one, open or close an archive, get to the table of favorite archives - Favorites (formed by the user), view the properties of the current zip file, put an icon with a link to it on the desktop, and also do anything with the archive itself (transfer , copy, rename, delete, print and link to email services). Those who like to go everywhere hand in hand with the "hint wizard" can select the Wizard mode (there is also a separate button). The Actions menu opens up a wide range of options (most of which are duplicated by special buttons): add (Add), delete (Delete), unpack (Extract), view individual files in the archive (View), select all files in the archive (Select All) and cancel this action (Ivert Selection). It is also possible to check the archived files for virus detection (Virus Scan) (of course, this requires that one of the antivirus programs). You can make an archive "self-extracting", i.e. turn it into an executable exe file, by selecting the Make .Exe File command (control is transferred to WinZip program Self Extractor). If at the same time you want to "spread" the self-extracting archive on floppy disks, select the Safe spanning method option. Among additional features this menu: convert archive file to universal format forwarding by e-mail to UUE, pre-checking the archive for unpacking, preparing a comment for the archive, creating a separate menu in the Start > Programs section (CheckOut).
On the menu

Slide 19

Comparative test of performance and compression ratio of the most popular archivers (WINRAR, WINZIP, RAR).
On the menu
Archivers Compression time (in sec.) Final volume Compression ratio (in %)
WINRAR 851 276 MB (289,776,458 bytes) 97.08
WINZIP 59 276 MB (290 110 408 bytes) 97.19
RAR 245 167 MB (176,049,935 bytes) 58.98
Initial size 284 MB (298,502,392 bytes)

Slide 20

14.11.16

Archiving

• What is a file?
• What are the types of files?
• How to determine file size?
• List the units of information.
• What are the storage media?
• What types computer programs You know?

Archiving

Archiving is packing (compressing) a file or a group of files in order to reduce the space they take up on a disk.

Archiver- This is a program that allows, through the use of special methods of information compression, to create copies of files smaller, as well as combine copies of several files into one archive file, from which you can, if necessary, extract the files in their original form.

Archiving is the process of data compression.

• create rar archives and extract files from them;
• create self-extracting archives - the archive file in this case will have an .exe extension and will run as regular program. Files from such an archive can be extracted on any computer by running the program;
• create multi-volume archives, which allows you to place a large archive on several media of limited capacity.
• set a password for the archive - in this case, an outsider will only be able to view the list of archive files, but will not be able to unpack the compressed data;
• reduce the file size for sending by e-mail, provides a compression ratio of up to 95%.

• files
• folders
• discs

Purpose of archiving

Compressing files to save memory

Compressing files and folders necessary for

• their transportation, Reserve copy, to exchange information over the Internet. Disc seal
• their transportation,
• for backup,
• to exchange information over the Internet. Disc seal are used to improve the efficiency of using their working space, usually for disks of insufficient capacity.

Types of archivers

File archivers

Pack one or more files into a single archive file, the size of which is usually less than the total size source files, but you cannot use the packed programs or data while they are in the archive until they are unpacked. To unpack an archive file, the same archiver is usually used.

Software archivers

They allow you to pack one single file at a time - an EXE-type executable program, but in such a way that the archived program will self-extract in RAM immediately after it is launched for execution and immediately begin work.

Disk archivers

Allow programmatically increase available hard disk space. A typical disk archiver is a resident driver that silently archives any information written to disk and decompresses it back when read. However, file read/write operations slow down somewhat because the processor takes time to pack and unpack.

Common archivers

There are different archiving programs that differ in the format of archive files, speed, degree of compression of files when placed in an archive, and ease of use. The most common archiving programs have approximately the same capabilities and none of them is superior to others in all respects: some programs work faster, others provide a better degree of file compression. Even if we compare programs only in terms of compression ratio, there is no leader among them: different files are better compressed by different programs.

The principle of operation of archivers

is based on searching for "redundant" information in the file and its subsequent encoding in order to obtain the minimum volume. The most well-known method of archiving files is compression of sequences of identical characters. For example, inside your file are sequences of bytes that are frequently repeated. Instead of storing each byte, the number of repeated characters and their position is fixed. For example, a file to be archived is 15 bytes long and consists of the following characters:

B B B B B L L L L L A A A A A

In hexadecimal this would be

42 42 42 42 42 4C 4C 4C 4C 4C 41 41 41 41 41

The archiver can represent this file in the following form (hexadecimal):

01 05 42 06 05 4C 0A 05 41

This means: from the first position, the character "B" is repeated 5 times, from position 6, the character "L" is repeated five times, and from position 11, the character "A" is repeated five times. To store a file in this form, only 9 bytes are required, which is 6 bytes less than the original one.

The described method is a simple and very effective way to compress files.

The principle of operation of archivers

A more sophisticated method of data compression is the so-called optimal prefix code and in particular, variable length encoding (Huffman algorithm). A variable length code allows the most frequently occurring characters and groups of characters to be written in just a few bits, while rare characters and phrases will be written in longer bit strings. For example, in any English text, the letter E occurs more often than Z, and X and Q. Thus, using a special lookup table, you can encode each letter E with fewer bits and use a longer code for rarer letters.

Some archivers work on the basis of the Lempel-Ziv algorithm. These archivers are classified as adaptive dictionary encoders , in which text strings are replaced with pointers to identical strings found earlier in the text. For example, all the words in a book can be represented as page numbers and line numbers in a dictionary.

Information compaction methods

Algorithm

Huffman algorithm

Algorithm

or Basic compression algorithms

RLE algorithm

uses the principle of identifying repeating sequences and replacing them with a simple structure that indicates the data code and the repetition factor.

Compression writes a sequence of two repeating values: the repeated value and the number of repetitions.

Example

Original sequence: 3, 3, 12, 12, 12, 0, 0, 0, 0 Compressed information: 3, 2, 12, 3, 0, 4 Compression ratio: 6/9*100% = 67%.

Algorithm RLE(Run-Length Encoding) Speaking of compression algorithms, we mean reversible algorithms.

KWE algorithm

involves the use of a dictionary in which each word corresponds to a two-byte code. Compression efficiency increases with the size of the encoded text.

KWE (Keyword Encoding) algorithm

Huffman algorithm

involves encoding not by bytes, but by bit groups. It can be divided into 3 main stages:

• The frequency of repetition of each of the occurring characters is revealed.
• The more common a character is, the fewer bits it encodes.
• A lookup table is attached to the encoded sequence.

The compression ratio depends on

Used archiver

Compression method

Type

source file

• Archive- this is a file containing one or more files in a compressed (packed) form. Archive filenames can have extensions. zip , arj , rar , arc , etc. depending on the type of archiver in which they were created.
• Archiver- a special program with which you can compress files, place "long" archives on floppy disks, view the contents of archives, control their integrity, unpack archives, etc.
• Archives are created in order to reduce the size of the original file (saving disk space) and increase the speed of copying (especially when sending over the Internet and e-mail).
• Self-extracting archive- this is an executable program (file.exe), which includes both an archive and a program for unpacking it. This is especially advantageous when you do not know if there is an appropriate archive program on the computer on which you are decompressing.
• Distributed archives - it is supposed to transfer a large amount of information on low-capacity media.

Compression reversibility

If data content changes during data compression, the compression method is irreversible.

This method is called lossless compression.

Lossless compression formats

Lossy compression formats

• JPG graphics
• MPG video
• MP3 sound

• GIF, TIF, PCX
• ZIP, ARJ, RAR

• What is archiving?
• Why is archiving necessary?
• Why is it possible to reduce file size?
• What files do not make sense to archive?
• Why does it make sense to pack it into an archive before sending a text file by e-mail?
• What is an archiver?
• List the types of archivers.
• What 3 principles of work of archivers do you know?
• What does multi-volume archive mean?
• What is a self-extracting archive?
• What is the compression ratio of a file?
• Why do you need a backup?
• What is unzipping?

Archivers.

back

• What are archivers?
• Information compression.
• The main types of archivers.
• Self-extracting archives.
• What are multi-volume archives?

What are archivers?

back

Archivers are one of the most common utility programs designed for archiving and packaging files by compressing information.

archive file- this is a specially organized file containing one or more files in compressed or uncompressed form and service information (file names, date and time of their creation, size, etc.)

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Information compression.

back

Information compression- this is the process of converting information stored in a file to a form in which redundancy in its representation is reduced and, accordingly, less memory is required for storage

Information is compressed by eliminating redundancy different ways, for example, by simplifying the codes, eliminating constant bits from them, or representing repeated characters as a repetition factor.

For example, if the word "mother" occurs 1000 times in a text file, then the size is NOT compressed file is equal to 4000 bytes (4 bytes x 1000 times = 4000 bytes). If this file is compressed, then the archiver will write the word "mother" to the archive only once, but at the same time note that this word occurs 4000 times. Thus our text file will shrink approximately 500 times.

Information compression.

back

Degree of information compression- This is one of the most important indicators of the archive. It is characterized by the coefficient K c, defined as the ratio of the volume of the compressed file V c to the volume of the original file V 0 , expressed as a percentage (%).

The compression ratio depends on:

Compresses best:

• graphic files (*.bmp, *.png and some others)
• text files (*.doc, *.txt, *.xls, etc.)

• program used
• compression method
• source file type

Doesn't compress well files of executable programs (*.exe, *.com) and load modules (*.dll, for example) - 60-90%.

Almost never compress archive files. Try to explain.

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Archivers.

back

Archivers are programs that pack and unpack files.

Package(archiving) – placing (loading) source files into compressed or uncompressed archive files.

Unboxing(unzipping) - the process of restoring files from an archive in exactly the same form as they had before being loaded into the archive. When unpacking, the files are extracted from the archive and placed on disk or in RAM.

The most common archivers at present are:

Name

supported archive formats

*.rar, *.arj, *.ice, *.pak, *.zip, *.exe (self-extracting) and many more

*.ace, *.rar, *.arj, *.ice, *.pak, *.zip, *.exe (self-extracting) and many more

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Context menu.

Archivers.

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Today, most users work with WinACE and WinRAR, 7-Zip (and the latter are developed in Russia). This is due to the fact that both of these archivers use better compression methods than WinZIP. In addition, they allow you to create self-extracting archives.

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back

The main features of the program:

• the ability to work in two modes - a full-screen interactive interface and a conventional command line interface
• support for other types of archives (*.rar, *.arj), viewing their contents, changing and converting
• using a highly efficient solid (continuous) compression method, increasing the compression ratio by 10-50%
• the ability to create self-extracting and multi-volume archives
• protection of the archive from changes with a password (blocking)
• possibility of partial or full recovery damaged archives
• many other functions of the archiver (more than 15) can be found in reference guide

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The 7-Zip archiver supports many archive formats. It has a simple and intuitive interface: you can work in single disk mode, or you can work with archives / files using 2 disk panels at once (similar to a file manager).

In this program, it is worth noting its own format for creating archives 7 z. The compression ratio in it is better than that of the popular ZIP and RAR archive formats, however, the process of archiving files in this format is longer.

7-Zip supports the following archive formats: 7z, ZIP, RAR, ARJ, GZIP, BZIP2, TAR, CPIO, RPM, and DEB. It is possible to create self-extracting archives.

Self-extracting archives.

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Self-extracting archives- this is a bootable, executable module that is capable of independently unzipping the files contained in it without using an archiver program.

created in

SFX archive,

created in

Archiver programs allow you to create archive files that do not require any programs to extract, because the archive files themselves may contain an unpacking program. Such files are called self-extracting archives. Most often, such archives have the *.exe extension. Such archives are called - SFX-archives (from S el F -e X tracting).

This addition, called the SFX module, increases the size of the archive by 35 kilobytes. For comparison: a new formatted 3.5” floppy has 1400 kilobytes free.

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Multi-volume archives.

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One of the most important advantages of the WinRAR archiver is the ability to create multi-volume archives, i.e. archives that require two or more floppy disks. Each disk contains one or more volumes.

Also, the ability to work with multi-volume archives can be useful when working on the Internet, more precisely when working with email when there is an email size limit.

Multi-volume archive- this is an archive "split" into a number of parts (volumes), and: the first volume of a multi-volume archive receives the extension *.rar, and the extensions of subsequent volumes are numbered as *.r00, *.r01, *.r02, etc. to *.r99

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Continuous Archive

back

Continuous Archive is a RAR archive packed special in a way that treats all compressed files as one serial data stream. Continuous archiving is supported only in the RAR format, there is no such type of archive for the ZIP format. The compression method for RAR archives - regular or continuous - is user-selectable.

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 backup has some flaws :

· update continuous archives (i.e. adding files to an existing archive or deleting them) is slower than normal ones;

· to to extract a single file from a contiguous archive, one has to parse all previous archived 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 first files are extracted from a continuous archive, then in this case the unpacking speed is almost equal to the unpacking speed of a regular archive;

· If in a continuous archive, if a file is corrupted, then all the files following it will not be able to be extracted.

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Presentation on the topic: Archivers

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Description of the slide:

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Description of the slide:

What are archivers? Archivers are one of the most common utility programs designed for archiving and packaging files by compressing information. An archive file is a specially organized file that contains one or more files in compressed or uncompressed form and service information (file names, date and time their creation, size, etc.)

slide number 3

Description of the slide:

Information compression. Information compression is the process of converting information stored in a file to a form that reduces redundancy in its representation and, accordingly, requires less memory for storage. Information is compressed by eliminating information redundancy in various ways, for example, by simplifying codes, excluding constant bits from them. or representing repeated characters as a repetition factor. Read more…

slide number 4

Description of the slide:

Information compression. Information compression is the process of converting information stored in a file to a form that reduces redundancy in its representation and, accordingly, requires less memory for storage. Information is compressed by eliminating redundancy in various ways, for example, by simplifying codes, eliminating constant bits from them, or representing repeated characters as a repetition factor. More... For example, if the word "mom" occurs 1000 times in a text file, then the size of the UNCOMPRESSED file is 4000 bytes (4 bytes x 1000 times = 4000 bytes). If this file is compressed, then the archiver will write the word "mother" to the archive only once, but at the same time note that this word occurs 4000 times. Thus, our text file will be compressed approximately 500 times.

slide number 5

Description of the slide:

Information compression. The degree of information compression is one of the most important indicators of the archive. Characterized by the Kc coefficient, defined as the ratio of the volume of the compressed file Vc to the volume of the source file V0, expressed as a percentage (%). Files of executable programs (*.exe, *.com) and load modules (*.dll, for example) are poorly compressed - 60 -90%. Archive files are almost not compressed. Try to explain.

slide number 6

Description of the slide:

Archivers. Archivers are programs that package and unpack files. Packing (archiving) - placing (loading) source files in compressed or uncompressed archive files. Unpacking (unzipping) - the process of restoring files from an archive exactly as they were before loading to the archive. When unpacking, files are extracted from the archive and placed on disk or in RAM. The most common archivers at present are:

slide number 7

Description of the slide:

Archivers. Today, most users work with WinACE and WinRAR (the latter was developed in Russia). This is due to the fact that both of these archivers use better compression methods than WinZIP. In addition, they allow you to create self-extracting archives.

slide number 8

Description of the slide:

winrar. The main features of the program: the ability to work in two modes - a full-screen interactive interface and a conventional command line interface; support for other types of archives (*.rar, *.arj), viewing their contents, changing and converting; compression by 10-50% more... the ability to create self-extracting and multi-volume archives protection of the archive from changes with a password (blocking) the ability to partially or completely restore damaged archives many other functions of the archiver (more than 15) can be found in the reference manual

slide number 9

Description of the slide:

Self-extracting archives. Self-extracting archives is a bootable, executable module that is capable of independently unzipping the files contained in it without using an archiver program. Archiver programs allow you to create archive files that do not require any programs to extract, because. the archive files themselves may contain an unpacking program. Such files are called self-extracting archives. Most often, such archives have the *.exe extension. Such archives are called SFX archives (from SelF-eXtracting). This addition, called the SFX module, increases the size of the archive by 35 kilobytes. For comparison: a new formatted 3.5” floppy has 1400 kilobytes free.

slide number 10

Description of the slide:

Multi-volume archives. One of the most important advantages of the WinRAR archiver is the ability to create multi-volume archives, i.e. archives that require two or more floppy disks. Each disk contains one or more volumes. Also, the ability to work with multi-volume archives can be useful when working on the Internet, more precisely when working with e-mail, when there is a limit on the size of letters. receives the extension *.rar, and the extensions of subsequent volumes are numbered as *.r00, *.r01, *.r02, etc. to *.r99

slide number 11

Description of the slide:

Non-stop archive A non-stop archive is a RAR archive packaged 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, there is no such type of archive for the ZIP format. The compression method for RAR archives - normal or continuous - is selected by the user. Continuous archiving significantly increases the compression ratio, especially when adding a significant number of small files with similar content to the archive. However, you should keep in mind that continuous archiving also has some disadvantages: updating continuous archives (ie adding files to an existing archive or deleting them) is slower than regular ones; · to extract one file from a continuous archive, you have to analyze all the previous archived 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 first files are extracted from a continuous archive, then in this case the unpacking speed is almost equal to the unpacking speed of a regular archive; · if any file in a continuous archive is damaged, then all the files following it will not be able to be extracted.