What Are .ZIP and .7Z Files?

May 23, 2008 in Specific Computer Information
Tags: .7z, .7z file, .zip, .zip file, archive, compression, explain, explained, file, file archive, file compression

Who should read this:

Readers should want to know more about uploading and downloading files. Also if you receive e-mail attachments from friends or colleagues and you don’t know how to open them, this might help. This post mainly deals with the most popular form, .ZIP and the new form of compression, .7Z.

Nowadays .7Z files provide greater compression than traditional .ZIP files and the technology behind it is open source so this new file format should remain free for years to come.

7-Zip is the main program used for creating and extracting these new .7Z file types. 7-Zip is also backward compatible with almost all popular file compression formats. 7-Zip is free but has support for proprietary compression formats so the license is slightly restricted, mainly when it comes to .RAR support. 7-Zip does not provide .ACE support to lessen the license restrictions. It’s nothing to worry about unless you are using 7-Zip to manage .RAR archives. I prefer ICEOWS for that anyway.

If a file is extracted from a compressed archive (.7Z or .ZIP file) and that file is changed then the archive must be updated with the new/modified file. The original file inside the archive needs to be manually updated with the changed file by adding it back to the original archive for recompression. Otherwise the the original archive (.7Z or .ZIP file) will remain unchanged. Modifications to the content of files inside an archive cannot take place directly inside the .7Z or .ZIP file. It is a 3-step process. 1) Extract, 2) Change, 3) Update or Recompression.

iArchiver for the Mac is the way to go for .7Z support in Mac OS X. This tool will automatically convert from .ZIP to .7Z and convert from .7Z to .ZIP. A feature 7-Zip and many compression programs are without. On a Windows PC you must extract the .ZIP and recreate a .7Z file from the contents you extract.

Related Information:

.MP3 files are compressed .WAV files. Creating .MP3 files a cause a permanent loss of quality versus using a .WAV file. The raw audio format. A CD track is copied from the audio CD into a .WAV file. Depending on what program you are using to extract the audio (CDex or iTunes…) the resulting .MP3 or .MP4 file is created from a .WAV file that needs to be extracted from the CD first. You will see very little size reduction if you archive an .MP3 file into a .7Z or .ZIP file. Also you won’t be able to listen to a Zipped .MP3 files until it is first extracted from the archive.

.GIF, .JPG & .PNG files are compressed .BMP file with permanent quality loss.

An .MPG file is usually a compressed .AVI file with permanent quality loss.

Some Background On File Compression:

People used to call directly through their phone line to other local computers with dedicated phone lines before the Internet became popular. These Bulletin Board Systems or BBSes were usually place to download new software and games from. Most of these files were freely available but the authors encouraged payments by limiting features without registration or nagging until you purchase a valid license. Zipping the downloadable files was a popular way to save valuable hard disk space. Zipping files also makes the transmission of these files faster thus keeping the phone lines available for other users to dial in. In the case of a high speed connections, compressing files helps to save bandwidth and reduce line congestion (or lag).

A .ZIP file might also be used to hold a set of pictures or multiple related documents just to keep them together for e-mailing or backup. Almost any file can be Zipped.

For years pkzip.exe and pkunzip.exe were the commands needed to deal with .ZIP files. .ZIP files are a widely used file compression format and standard.

pkzip.exe was used to create a .ZIP file and pkunzip.exe was used to extract from a .ZIP file.

These programs were freely available but the author requested money. You could still use the programs for free without any interruptions. This concept of try before you buy is called Shareware. As the popularity of Shareware & use of the .ZIP format grew so did his company, PKWare, as did the protection of his intellectual property.

WinZip is Shareware as was PKZip but is not written by PKWare. WinZip is considered Nagware to be exact. WinZip is also commercially available and many corporations actually do purchase licenses to provide for better Windows-based .ZIP file management.