Archivers.

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

What are archivers?

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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.

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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 "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 shrink approximately 500 times.

Information compression.

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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.

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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:

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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 best practices compression, compared to WinZIP. In addition, they allow you to create self-extracting archives.

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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 complete recovery of damaged archives
• many other functions of the archiver (more than 15) can be found in the reference manual

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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 panels for disks at once (similar to file manager).

This program should be noted own format 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

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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 limitations :

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

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

An archiver program is a computer program that allows you to reduce the amount of information and store it without damaging this information. They are used for long-term storage of information in a compressed form, creating backups, and sending files over the network. There are various methods for archiving files, which differ in the degree of file compression, speed of execution, and other parameters.

There are different archivers. Here are some examples of RAR WinRAR (or as it is called "Winrar", Win-RAR) is one of the most convenient and powerful computer programs archiving for operating system Windows. The name of the program is derived from the words WIN (Windows) and RAR (Roshal ARchive). The author of the program is Evgeny Roshal, by the way, our compatriot. It has a very small size with a rich set of functions and speed. The current version at the time of writing - Winrar Winrar contains a special improved compression algorithm for multimedia files, object libraries and executable programs. Winrar provides the ability to recover damaged archives, encrypt, create multi-volume archives and many other useful and unique features. ZIP Appeared a new version programs for working with ZIP archives. CoffeeCup Free Zip Wizard 2.6 provides an easy way to create a ZIP archive, as well as extract and modify existing ZIP archives. All actions in the program are carried out using step-by-step Wizards that explain each stage of work, which allows you to quickly understand all the intricacies of archiving files. The program can create self-extracting archives, allows you to adjust the degree of file compression and set a password to open the archive. Using the built-in tools of CoffeeCup Free Zip Wizard 2.6, you can upload it to an FTP server immediately after creating an archive. In addition, there is a function to search for ZIP files on any drives connected to the computer.

7 Z 7-Zip 4.31 archiver that supports many archive formats. 7-Zip 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 7z archives. 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, CAB, RAR, ARJ, GZIP, BZIP2, TAR, CPIO, RPM and DEB. It is possible to create self-extracting archives

Principle of operation The principle of operation of archivers is based on the search for "redundant" information in a file and its subsequent coding in order to reduce the volume. When archiving, the degree of compression of files depends on its format. Archiver programs can reduce the file size to the smallest possible size. The interface of all modern archiver programs is very similar.

File archiving Start the WinRAR 3_0 archiver. Select files (mark a directory), activate the "Add" button on the program toolbar. When creating a new archive, you need to set the archiving parameters: specify the name of the archive file; storage space on disk select the archiving format (rar, zip, exe). choose one of six archiving methods: no compression - places files in an archive without packaging; high-speed - compresses poorly, but quickly; quick; normal - daily backup copy data; good; maximum - the best compression at a lower speed; choose the size of the dictionary. Values ​​64,128, 256, 512 more - better, but slower compression; select the size of splitting into multi-volume archives, usually for storage on floppy disks. Size KB;

It is possible to create a self-extracting file - SFX mode (SelF-tXtracting). no program is needed for unzipping, just run the file for execution, the file is executable and has the .exe extension. on the archive name and parameters panel, set: name of the archive file; archive storage location on disk (default); archive format; compression method; dictionary size (default); volume size; update method; archiving options. to extract files (catalog) you need to select the archive file, activate "Extract" on the program toolbar. By default, the archive is unpacked to the same directory.

A continuous 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 - 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, you should keep in mind that continuous backup also has some disadvantages: updating continuous backups (ie adding files to an existing archive or deleting them) is slower than regular backups; · 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.

OGAOU SPO "Belgorod Construction College"

Discipline lesson summary

"Computer science"

Topic: “Archivers. Archives and archiving: purpose, terms, definitions"

prepared

teacher information technologies

Chelombitko Elena Mikhailovna

Belgorod 2014

Lesson topic: Archivers. Archives and archiving: purpose, terms.

Lesson type: study of new educational material.

Type of lesson: lesson-lecture

The purpose of the lesson: ensure that students understand the concept of "archivers"; main operating modes of archivers; consider the advantages and disadvantages of a continuous archive; work at the right pace - take notes; to promote the education in students of attention, discipline.

Equipment: interactive whiteboard, lesson summary, presentation.

Lesson structure.

2. Familiarization with new educational material

3. Homework.

4. Summing up.

1. Organizational moment and goal setting.

1.1. Checking the readiness of the group for the lesson.

1.2. Greetings. I mark those who are absent in the journal.

Target: In today's lesson, you will learn what archivers are, why they are needed, what types of archives there are and what are their advantages.

2. Acquaintance with new educational material.

I tell and explain the material to the students, they write down the necessary information in a notebook. Questions are asked as the material is being explained.

Archivers - this is a specialized program designed for file compression, i.e. reducing their size or the disk space they occupy.

Archive - file created by the archiver.

Archiving - information compression process.

After compressing the size, the file can be significantly reduced - archive file. Before using such a file, it must be unzipped.

The main modes of operation of archivers:

1. Adding files to the archive.

2. Extracting the file from the archive.

3.Updating the archive.

4. Creation of self-extracting archives from existing ones.

5.Browse directories.

Types of archives:

1.Continuous archive - This is an archive with the extension . rar 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, there is no such type of archive for the ZIP format.

Some disadvantages of continuous archiving:

updating continuous archives is slower than usual;

to extract one file from a continuous archive, you have to analyze all the previous ones;

if any file in a continuous archive is corrupted, it will fail to extract all the files following it. Therefore, when saving a continuous archive, it is recommended to add information for recovery.

Continuous archives are preferred

use when:

the archive is supposed to be rarely updated;

it is planned to unpack the entire archive more often;

you need to achieve a tighter compression ratio, even at the expense of speed.

2. Volumes - these are fragments of the archive, consisting of several parts. Volumes are only supported in . rar. Volumes are used to store a large archive on multiple removable media.

Already created multi-volume archives cannot be modified.

To unpack volumes, you must start extracting from the first volume.

Recovery volumes are a special file with a . rev created by WinRAR and are used to recreate missing and damaged volumes in a multi-volume archive.

To WinRAR recreated the missing and damaged volumes by clicking on the .rev file. If WinRAR does not find the next volume during unpacking, but finds the required number of .rev files, then it will recreate the missing volumes automatically.

3.Self-extracting archive - this is the archive to which the executable is attached. This module allows you to extract files by simply launching the archive like a normal program.

Self-extracting archives, like any other executable files, usually have a . exe.

Self-extracting archives are useful in cases where you need to transfer the archive, but you are not sure that the recipient has the appropriate archiver for unpacking.

3. Homework.

Read the lecture notes.

4. Summing up.

In today's lesson, we have studied the concepts of "archivers", "archive", "archiving", what they are used for, types of archives.