Although storage media have become quite large these days, it is often necessary to reduce the file size, for example, in order to send it by email.

You will need

• There are quite a few programs for reducing file sizes. From free utilities The most commonly used program is 7-zip. It is convenient because it has the ability to work with most of the archiving algorithms of various other programs.

Instructions

An archiver is a program that, using information compression methods, allows you to create smaller copies of files, as well as combine copies of several files into one archive file. Let's consider the classification of archivers. 1. File archivers. 2. Compressors.

Many people have probably encountered file archivers. It is enough to list their names: ZIP, RAR, ARJ. Such archivers allow you to pack one or more files into a single archive file. The archive size is usually less than the total size of the source files. Compressors compress only one executable file (EXE type) at a time in such a way that after launch the program self-extracts into random access memory and continues his work. These are programs such as PKLITE, RAC, LZEXE. Today the leader is the UPX program.

Redundancy Editors who work with text, graphics, audio and other information encode it in the most natural, but not the most economical way. Indeed, if you carefully look at any text, you will notice that such letters “a” and “o” are found in it much more often than “yu” and “u”. The same can be said for letter combinations. In the pictures, the colors of neighboring dots are in most cases similar in shade. Likewise, in any sequence of information, some combinations occur much more often than others.

Redundancy All this leads to the fact that in the files that store this information, some combinations of 0 and 1 are much more common than others. In such cases, they say that the information is redundant, and it is possible to recode the contents of the file, reducing its size. For compression, it is enough to follow the rule: the more often a combination occurs, the shorter a combination of 0 and 1 it can be recoded. Of course, the program must do this.

Archivers When compressing, you can reduce the file size several times, which gives noticeable memory savings. For example: WinRar and WinZip Start All Programs WinRAR archivers WinRAR One of the main characteristics of archivers is the degree of information compression. It can be determined by the formula:

How does the archiver work? The easiest way to archive text information- replacing standard phrases with the corresponding bytes; a byte will encode not just one character, but an entire phrase! The file size will be significantly reduced. Graphic files can be compressed like this. The colors of the drawings are encoded in bytes. Regions of the same color contain sequences of bytes. These are the sequences we encode with just two bytes: the byte is the sample and the byte is the number of samples. Thus, the file size is reduced several times.

Lesson objectives:

• Consolidating students' knowledge, skills and abilities about archiving files, getting acquainted with the concept of redundancy, teaching how to archive and unpack various (text and graphic) files, giving the basic concepts necessary for competent work on a computer.
• Fostering students’ information culture, attentiveness, accuracy, discipline, and perseverance.
• Development of cognitive interests, computer skills, self-control, note-taking skills.

Equipment:

• board,
• computer,
• presentation.

Lesson plan:

1. Org. moment. (1 min)
2. Testing and updating knowledge. (5 minutes)
3. Practical part. (15 minutes)
4. The theoretical part - working with the presentation. (10 min)
5. D/z. (2 minutes)
6. Questions from students. (5 minutes)
7. Lesson summary. (2 minutes)

During the classes

I. Org. moment.

Greetings, checking those present. Explanation of the lesson.

II. Testing and updating knowledge.

In order to check how you have mastered the topics of previous lessons, I suggest you take a short test and evaluate your knowledge. Students take a test.

Add:

Safety precautions in the classroom.

Theoretical part.

Editors working with text, graphics, audio and other information encode it in the most natural, but not the most economical way.

Indeed, if you carefully look at any text, you will notice that such letters “a” and “o” are found in it much more often than “yu” and “u”. The same can be said for letter combinations.

In the pictures, the colors of neighboring dots are in most cases similar in shade. Likewise, in any sequence of information, some combinations occur much more often than others.

All this leads to the fact that in the files that store this information, some combinations of 0 and 1 are much more common than others. In such cases, they say that the information is redundant, and it is possible to recode the contents of the file, reducing its size.

For compression, it is enough to follow the rule: the more often a combination occurs, the shorter a combination of 0 and 1 it can be recoded. Of course, the program must do this.

Programs that perform compression (packing files) are called archivers.

Many different archivers have been created, the most common of which are WinRar and WinZip; Windows OS also includes the Data Archiving utility program.

When choosing an archiver, you need to be guided by its versatility and reliability, but, of course, do not forget about the main parameters - quality and compression speed.

When compressing, you can reduce the file size several times, which gives noticeable memory savings. This is especially valuable when sending files over the Internet or placing them on small media, such as floppy disks.

If you try to repeat the compression procedure, there will be no effect, since redundancy of information is mainly eliminated during the first packaging.

The information packed by the archiver is stored in the most economical form, but it is encoded in an artificial way, so before opening the contents of the file, it is necessary to re-encode the file (usually say: unpack, unzip, restore the file).

Basic actions when working with archives:

• creating a new archive;
• adding files to the archive;
• viewing archive contents;
• extracting files from the archive;
• viewing a file in the archive;
• deleting files from the archive.

In this lesson we will work with one of the most popular archiving programs WinRAR, all copyrights of WinRAR are exclusively owned by the author of the program, Russian programmer Alexander Roshal.

WinRAR can be used in two ways: in graphical shell mode with a standard Windows interface and in command line. To use WinRAR in shell mode, double-click on the WinRAR icon - you will then be able to use buttons and menus to archive and extract files.

III. Laboratory work in WINDOWS "Archiving files using the WINRAR program."

Purpose of the work: to study the steps to pack files into an archive and extract files from the archive using Winrar programs. Compare zipped text and graphic files.

1. Find out the size of the PAC1 (application1) folder in bytes

• Select folder PAC 1
• Call context menu
• Run the Properties command
• Read file size in bytes and write it to notebook Vfolders=

Pack the PAC1 folder into the pac1.rar archive

• Select folder
• Call context menu
• Run the WinRara Add to archive command:
• In the dialog box, select the rar format, using the Browse button: open the folder C:ARHIV

(as a result, an archive file should appear in the folder)

Find out the size of the archive file in bytes

• Open the ARHIV folder, select the archive name pac1.rar
• Call context menu
• Run the Properties command
• Read the size of an archive file and write it down in a notebook V archive=

Use the calculator program by loading it according to the STARTUP scheme PROGRAMSa STANDARDa CALCULATOR

Do similar work with the PAC 2 folder (Appendix 2) and find k2

Compare the results obtained k1 and k2, draw appropriate conclusions.

Call the teacher to check your work results

Now complete the tasks on one's own:

Create 2 archives.

Extract the file from the Wind_lecture_Beginner.rar archive.

Download several zipped files from the Internet to your folder and unzip them.

Conclusion by laboratory work: It is not rational to archive all types of files in order to reduce their size. An example would be the drawing in JPEG format, audio in MP3 format and others.

Work in groups:

Questions on the topic "Archiving":

1. Why is it possible to reduce file sizes?
2. What is archiving?
3. What files do not make sense to archive?
4. Why before shipment? text file by email, does it make sense to pre-pack it into an archive?
5. Is it possible to archive the same file several times?

Additionally:

1. Where in life is packaging (compression) used? Which material is easier to pack?
2. Give recommendations to a novice PC user about archiving files. Where to purchase the program and the need for packaging files.

Discussion of issues.

Know what archivers are and their purpose, be able to pack and unpack files in archives. Additional task: learn to create self-extracting archives. Email the zipped file to my address

VI. Questions from students.

Answers to student questions.

VII. Lesson summary.

Summing up the lesson. Grading.

During the lesson, we got acquainted with archivers and their purpose, and learned how to work with an archiver.

Thanks everyone for the lesson!!!

1. 1. Dolinin A.A., teacher of computer science and ICT MBOU "Urenskaya secondary school No. 1" File compression. Archivers.
2. 2. Redundancy Editors working with text, graphics, audio and other information encode it in the most natural, but not the most economical way.
3. 3. Redundancy All this leads to the fact that in the files storing this information, some combinations of 0 and 1 are much more common than others. In such cases, they say that the information is redundant, and it is possible to recode the contents of the file, reducing its size.
4. For compression, it is enough to follow the rule: the more often a combination occurs, the shorter a combination of 0 and 1 it can be recoded. Of course, the program must do this. 4. 4 Archiving and compressing files Archiving - creation backups
5. (on CD, DVD). Goals:  save data in case of disk failure  combine a group of files into one archive  encrypt data with a password Compressing files is reducing their size. Goals:  reduce the space that files occupy on disk  reduce the amount of data for transmission over the Internet Types of compression:  lossless: a compressed file can be restored in its original form, knowing the compression algorithm ▫ texts ▫ programs ▫ data  lossy: when compressed, part information is irretrievably lost photos (*.jpg) sound (*.mp3) video (*.mpg)
6. 5. Why can files be compressed? RLE algorithm (Run Length Encoding, encoding of chains of identical characters, used for *.bmp pictures) A ​​A … A B B … B 100 100 200 bytes File qq.txt File qq.rle (compressed) A 100 B 100 4 bytes Lossy compression or without?? 50 times compression! Compression is possible if there are repeated characters or strings of characters in the data, compression “eliminates” this redundancy.
7. 6. 6 Why can files be compressed? General approach:  find repeating strings of characters in the data  designate them with short codes (bit codes, of different lengths)  write a dictionary at the beginning of the compressed file Effective algorithms:  Huffman algorithm  LZW (Lempela-Ziv-Welch) algorithm  PPM algorithm (WinRAR) Compressed good bad  random data  programs (*.exe)  archives (*.zip, *.rar)  compressed pictures (*.gif, *.jpg, *.png, *.tif, …)  compressed audio (* .mp3, *.wma)  compressed video (*.mpg, *.wmv)  texts (*.txt)  documents (*.doc, *.xls)  uncompressed pictures (*.bmp)  uncompressed audio (* .wav)  uncompressed video (*.avi)
8. 7. An archiver is a utility program designed to compress (compress) files, i.e. to reduce their size and the disk space they occupy. Backup – creating archived copies of a file or group of files.
9. 9. Creating backup copies of documents.
10. Creation of electronic archives;
11. Transfer data from one PC to another.
12. Transferring data over the network. Purposes of using archivers:
13. 10. FUNCTIONS OF ARCHIVERS PROGRAMS: create archives and extract files from them;

add, extract, or delete individual files or groups of files from the archive; create self-extracting archives; create multi-volume archives;

Thus, archiving files is a process of reducing the size in bytes. The user does not notice the action taking place, working with the archive as with a regular folder. However, in fact, the difference in volume can be very significant, which is especially noticeable against the background of texts and tables. They can be reduced tens of times, losing most of their volume. However, individual files practically cannot be compressed, since they have already undergone similar processing. This, of course, primarily applies to certain music and image formats.

File archiving is most widely used when sending over local and global networks to reduce the load on them. The transfer in this case is much faster. In addition, at Email There are restrictions on the amount of information transferred, so data compression can be very useful here too. It is also quite convenient that a large number of files can be combined into one archive, which will be very easy to work with. The entire process is controlled by one program. With its help, it is possible to perform compression without any skills.

Thanks to the program, file archiving is completed literally in a matter of seconds, but first it must be found and installed on the computer. Although today many OS contain an archiver that allows you to pack and unpack certain types of data. Next, files that are to be archived are selected. By right-clicking on the selected files, you can quickly add them to the archive. At the last stage, the program requests the name and location of the compressed files. Unpacking is performed by two left-clicks on the archive.

Sometimes you may need to compress files using custom settings. Then these applications can provide a set of different settings. For example, the user can specify the creation of a password for the archive, format, etc. Among such functions is the ability to create self-extracting and multi-volume archives. The first of them have a special module, thanks to which it is possible to extract data by simply launching the application. In this case, there is no need to have an archiver on local computer. As for multi-volume archives, they allow you to divide the compressed file into separate parts.