How do compressed zip files work

Each word in this file appears twice. Now, if each letter and space in the sentence equals one unit of memory, then the entire file size would be units. But you can create a numbered code to express the data in a different way:.

Or to put it a different way, both sentences would now read: This means that the initial file size of units is reduced to 18 units, which is a massive savings.

The ZIP file format uses lossless compression algorithms to do exactly that. It allows you to express the same information in a more efficient way by removing the redundant data from the file. This also means it is faster to send a ZIP file. There are a broad range of potential uses for zipped files in a business setting. Being able to send large numbers of files over email is imperative. Say you need to send a big batch of files to a colleague or client.

If you try to send them all at once in an email attachment, you will get an error message because of file size. So you could try to send each file as in separate emails. But this is time consuming, labor intensive, and could lead to duplicate files. To send all the files in one email, you can zip them and attach this single ZIP file to your email. Your recipient can then unzip the file by downloading and clicking. You should also consider any potential storage saving. Zipping your files can help to reduce the amount of space they use on your computer's hard drive.

You can find more information on how to zip files here. So we've compressed the total file size from 79 units to 59 units! This is just one way of compressing the phrase, and not necessarily the most efficient one.

See if you can find a better way! So how good is this system? The file-reduction ratio depends on a number of factors, including file type, file size and compression scheme. In most languages of the world, certain letters and words often appear together in the same pattern. Because of this high rate of redundancy, text files compress very well.

A reduction of 50 percent or more is typical for a good-sized text file. Most programming languages are also very redundant because they use a relatively small collection of commands, which frequently go together in a set pattern. Files that include a lot of unique information, such as graphics or MP3 files , cannot be compressed much with this system because they don't repeat many patterns more on this in the next section.

If a file has a lot of repeated patterns, the rate of reduction typically increases with file size. You can see this just by looking at our example -- if we had more of Kennedy's speech, we would be able to refer to the patterns in our dictionary more often, and so get more out of each entry's file space. Also, more pervasive patterns might emerge in the longer work, allowing us to create a more efficient dictionary.

This efficiency also depends on the specific algorithm used by the compression program. Some programs are particularly suited to picking up patterns in certain types of files, and so may compress them more succinctly. Others have dictionaries within dictionaries, which might compress efficiently for larger files but not for smaller ones.

While all compression programs of this sort work with the same basic idea, there is actually a good deal of variation in the manner of execution. Programmers are always trying to build a better system. The type of compression we've been discussing here is called lossless compression , because it lets you recreate the original file exactly.

All lossless compression is based on the idea of breaking a file into a "smaller" form for transmission or storage and then putting it back together on the other end so it can be used again.

Lossy compression works very differently. These programs simply eliminate "unnecessary" bits of information, tailoring the file so that it is smaller. This type of compression is used a lot for reducing the file size of bitmap pictures, which tend to be fairly bulky. To see how this works, let's consider how your computer might compress a scanned photograph.

A lossless compression program can't do much with this type of file. While large parts of the picture may look the same -- the whole sky is blue, for example -- most of the individual pixels are a little bit different. To make this picture smaller without compromising the resolution, you have to change the color value for certain pixels.

If the picture had a lot of blue sky, the program would pick one color of blue that could be used for every pixel. Locate the zipped folder that you want to unzip extract files or folders from.

Do one of the following: To unzip a single file or folder, open the zipped folder, then drag the file or folder from the zipped folder to a new location. Notes: To add files or folders to a zipped folder you created earlier, drag them to the zipped folder. Need more help?

Join the discussion. Was this information helpful? Yes No. Thank you! Any more feedback? This is where the definition of a zip file ends for most people. What you may not realize is that you can do much more than just compress and combine files with zip archives. To create a zip file, right-click in a blank area on your desktop or in explorer, go to new, and select Compressed zipped Folder.

With the zip file created, just select and drag your files into the zip folder. As you can see in the screenshot, the files are copied into the zip folder, and not moved or deleted from their original location.

Now, you can transfer, backup, or do whatever else you want with your zipped contents. A new window will open up and you can select where you want the files to be extracted. By default, it will extract the contents to the same directory in which your zip file resides.

Just hit extract and a folder will be created that has all of the zipped files in it. There are a bunch of programs out there that offer additional functions for zip files, but one of the most lightweight, feature-packed, and efficient is 7-Zip.

Click that link to be taken to their website and download the latest version of the program. Installation is straightforward, just accept the license agreement and click next until 7-Zip is installed. After that, you should be able to highlight files, right-click them, and add them to a zip archive with 7-Zip. Remember to use a strong password, so brute force and dictionary attacks become useless. ZipCrypto vs. ZipCrypto is weak but has fewer compatibility issues.

AES is much stronger but only works with newer systems or with those that have 7-Zip installed. Try to choose AES when possible. Encrypting file names — Sometimes file names can be just as important as the contents inside of a file. Other times, maybe not. That problem can be solved by creating a self-extracting archive, giving you the best of both worlds.

If, for some reason, you NEED to use a. A self-extracting archive is nothing more than a usual zip file, but with an. Executing the file will automatically start the extraction process. Advantages — There are two big advantages to self-extracting archives.

First, you can utilize the.