While surfing the web, you will undoubtedly find media files and software you want to download. Since applications and media files, especially full-length movies, can be very large, downloading them may take a very long time depending on the speed of your Internet connection. Websites that host these types of downloadable files compressed into an archive format, and the zip format is the most popular archive file format.
How Compression Works
To speed things up and make efficient use of disk space, many large files are compressed. File compression reduces the size of a file, shortening the time it takes to download. Compression software uses complex mathematical equations to scan a file for repeating patterns in the data. It replaces the data with smaller codes that take up less room. For example, one way that compression software works is to replace repeating text characters with a code that also notes the locations of those characters in the data. With a picture, it would find all of the red pieces, for example, and replace them with a code.
Viewing Compressed Files
To view compressed archive files, you need to use an operating system with built-in capability to open zip files or a compression and decompression utility program that know how to deal with archive file formats.
Most of the files you encounter on the Web are either text, graphics, audio, or video files. Some may be compressed, others not. The most common compressed files are those with extensions such as .zip, .sit and .tar. These extensions represent popular compression formats for the PC, Macintosh, and Linux. They may be a single file or groups of files that have been bundled into a single archive. An archive file can sometimes contain any type of file and often contains software programs with related documentation.
Modern operating systems are generally capable of creating zip format archives and decompressing, or unzipping, zip files without the need to use any additional software.
- On a Windows PC, to create a zip file simply select the files you wish to compress in a Windows Explorer window, click on the Share tab on the menu ribbon, and select Zip.
- To decompress a zip file on a Windows PC, right-click on the zip file name, select Extract All, and follow the prompts.
Working with other types of archive files isn't as straightforward. However, there is a free utility program which can be used to work with many popular archive file formats including RAR, Zip, Tar, Gzip, and more. The application is called 7-Zip, but is only available for Windows. A port of 7-Zip for Mac OS X systems is called Keka, and unofficial versions of 7-Zip are also avialable for many Linux systems.
For more information about compression, read the Zip Definition in our glossary.
Frequently Asked Questions
Are zip files safe?
Because compressed files can contain any type of files, they are often used to spread a variety of malicious programs. This doesn't mean that compressed files are unsafe. As long as you know the contents of a compressed file, and get the file from a trusted source, they are perfectly safe. However, you should never open a compressed file you receive unexpectedly or download from a questionable source. In addition, make sure to keep your anti-virus software updated to help protect against malware infections.
I sent a zip file as an email attachment, but the recipient can't open it. What's going on?
Because archive file formats are so commonly used to transmit viruses, email service providers often disable archive files received as email attachments. While this can be annoying if you trust the email sender, its a necessary step in preventing the spread of computer viruses. Instead of sending archive files as an email attachment use a cloud-storage and file-sharing service such as Google Drive or Dropbox to transfer these types of files.