Informatics presentation "Archivers. Data Archiving"

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Data archiving

Archiving is the process of compressing one or more files in order to save memory and placing the compressed data in a single archive file. Data archiving is a reduction in the physical size of the files in which data is stored, without significant information loss.

Any of the archives has its own compression scale No compression - corresponds to the usual copying of files to an archive without compression High-speed compresses - relatively bad, but very fast. Fast - characterized by the fastest, but the least dense compression Normal - for daily backup of data. Provides high-quality and relatively fast archiving Good - compresses relatively quickly and efficiently Maximum - the highest possible compression is also the slowest compression method

Text files (in TXT, RTF, DOC format, etc.) are best archived. Excel spreadsheets Various databases. EXE program files They can be compressed several times, while they are completely and without errors "unpacked" at any desired moment.

Graphic files in .BMP format are best archived. But .JPG or .GIF picture files, .MP3 and .WMA music files, .AVI and .WMV video files are almost impossible to compress using an archiver, except perhaps just a little bit. In addition, there is no point in archiving the archive itself - there will be no compression.

Archivers are programs (a set of programs) that compress and restore compressed files in their original form. The process of compressing files is called archiving. The process of recovering compressed files is by unzipping.

WinRAR archiver WinRAR features: Allows you to unpack CAB, ARJ, JAR archives, etc. Provides data archiving in ZIP and RAR formats Provides full support for ZIP and RAR archives Supports drag & drop technology Provides recovery of physically damaged archives

WinRAR features: Provides the ability to create multi-volume archives, i.e. splits an archive into several parts (volumes) (for example, to burn a large archive to disks). Volume extensions: RAR, R01, R02, etc. With a self-extracting archive, the first volume has an EXE extension Creates self-extracting archives (SFX) regular and multi-volume archives, provides password protection Has recovery tools that allow you to restore missing parts of a multi-volume archive WinRAR is able to create an archive in two different formats: RAR and ZIP .

ZIP FORMAT The main advantage of the ZIP format is its popularity. For example, most archives on the Internet are ZIP archives. Therefore, it is best to send an email attachment in ZIP format. You can also send a self-extracting archive. Such an archive is a bit large, but can be extracted without external programs. Another benefit of ZIP is speed. ZIP archive is usually created faster than RAR.

The RAR format provides significantly better compression than ZIP. FORMAT.RAR Appearance WinRAR archiver

Thank you for your attention! The presentation was prepared by the Informatics teacher of the GAU SPO CO "College of Service and Tourism" Belousova Yu.V.

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Compression methods. Lossy compression In lossy compression, some information is lost, but this remains imperceptible to humans. For example: – When compressing video recordings of fast-moving objects, small details can be neglected; –When audio is compressed quiet sounds against the backdrop of loud; –When compressing graphics, replace the color of adjacent pixels with a similar value.

Huffman algorithm The Huffman method takes into account the probability of occurrence of objects and encodes them with codes of various lengths. For example, in the Russian alphabet, the letters O, E, A are common, F, C, Shch, E are rare. The more common a letter is, the shorter the code is used for it. This coding principle is used in Morse code: E A -E -

The Lempel-Ziv-Welch Algorithm The LZW (Lempel, Ziv, Welch) algorithm was invented in 1977 by mathematicians Abraham Lempel and Jakob Ziv, and further developed by Terry Welch in 1984. This method is the sliding window method. The algorithm encodes strings of characters (patterns), placing them in a table and replacing them with a shorter code. If such a chain occurs again, then not the chain itself will be placed in the output file, but its shorter code.

RLE algorithm RLE (Run Length Encoding) encoding of run lengths: a series of repeating bytes is replaced by one repeating byte and a counter of the number of repetitions ABCDEEGZHI?

WinRAR Features Full support for RAR and ZIP archives; Original highly efficient data compression algorithm; Unpacking CAB, ARJ, LZH, TAR, GZ, ACE, UUE, BZ2, JAR, ISO, 7Z, Z files; Creation of self-extracting, continuous and multi-volume archives; Adding additional information to archives to restore the archive in case of damage; The ability to protect the archive with a password.

Self-extracting archive A self-extracting archive (SFX self-extracting archive) is a *.exe file that combines an archive and an executable code for extracting it. Such archives, unlike ordinary ones, do not require a separate program to extract files from the archive, but they are larger. The use of self-extracting archives is useful when it is not known whether the user to whom the archive is being transferred has an appropriate unpacking program.

Non-stop archive A non-stop archive is an archive packed in such a way that all compressed files are treated as one continuous stream of data. The advantages of a continuous archive include a significant increase in the compression ratio. And the less the average size files, more files themselves and more similar files, the greater the compression ratio. The disadvantage of a continuous archive is that adding or removing files is slower than with regular archives.

Multi-volume archive A multi-volume archive is an archive divided into several parts (volumes). The need to split an archive into volumes arises, for example, when using floppy disks, if after compression the archive size exceeds the size of one floppy disk. The ability to work with multi-volume archives can be useful when working with email, When mail program allows you to attach only one file for sending, or the mail server allows you to attach a file of a limited size to a letter.

Extracting files from an archive using the Extract files… context menu allows you to specify the path for extraction. Extract to Current Folder will extract the files from the archive to the current folder. Extract to will create a folder with the name of the archive and place the extracted files there. Creating an archive using the context menu Add to archive... allows you to add files to an archive by specifying the location, name, archive format, compression method, and archiving parameters. Add to .rar archive will create an archive with the same name as the file or folder and default settings.

« Data archiving»

Basic concepts

• 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.
• Information compression

Archivers

• 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.)

Types of archivers

File archivers

Pack one or more files into a single archive file. 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.

Disk archivers

Allows you to programmatically increase the 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.

Information compression

• 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.

The compression ratio depends :

• program used
• compression method
• source file type

Best compressible files:

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

Poorly compressible files executable programs (*.exe, *.com) and load modules (*.dll, for example)

Types of archives

• self-extracting;
• multivolume;
• continuous.

SELF-EXTRACTING ARCHIVES

• 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. These archives are called SFX archives.

MULTIVOLUME ARCHIVES

• 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.

CONTINUOUS ARCHIVE

Continuous Archive- this is a RAR archive packed in a special way, in which all compressed files are considered only in the RAR format, for the ZIP format this type of archive does not exist. The compression method for RAR archives - normal or continuous - is user-selectable.

Winrar program

WinRAR is a high compression file archiver for Windows, one of the best archivers in terms of compression ratio to speed.

Key features

• Creating format archives RAR And ZIP .
• Unpacking format files CAB , ARJ , LZH , tar , GZ , ACE , UUE , BZ2 , JAR , ISO , 7z , Z .
• Special multimedia compression algorithm.
• Ability to work with files up to 8.589 trillion (10 12) gigabytes.
• Creation self-extracting , continuous And multivolume archives. Adding more to the archives recovery information archive in case of damage, including the creation of special recovery volumes that allow you to restore a multi-volume archive in case of damage to parts with information.

WinRar shell

Interface

Self extracting archive

Practical work“Using archiving programs”

• On desktop create a folder with the name of your group.
• Copy the Database document from the desktop into the folder, copy the pictures from the Pictures folder (3).
• Folder with the last name in the menu, select the function Add to archive. Create 2 archives.
• In the window that appears, specify: Archive name, format (Rar,)(Zip), specify the compression method (good, fast). Specify the SFX archive in the archiving parameters.

Unpacking files

• Select the archive and select the command "Extract files", "Extract to current folder" in the context menu

Crossword

• What is the name of placing source files in compressed or uncompressed archive files?.
• What is the process of converting information called?
• What is the name of the process of restoring files from an archive?
• What is the name of the program that packs and unpacks files?

Crossword

Thank you for your attention