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Creating & Opening Compressed Files

Overview

Compression lets you package a file or files such that they will be smaller than their actual size; this makes it easier to transfer files through email, for example, or conserve space for backups. Files cannot be used while they are compressed, so users must also be able to decompress files if they are to compress them in the first place. One of the most common compression methods in use today is ZIP format (.zip). Both Mac OS X and Windows XP have built-in support for creating and opening compressed ZIP archives.

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Mac OS X

In addition to ZIP, OS X supports a wide range of compression formats, including:

  • bzip2 (.bz, .bz2)
  • cpgz (cpio gziped)
  • cpio (.cpio)
  • gz (.gzip, .gz)
  • tar (.tar)
  • tgz (tar gziped)
  • tbz, tbz2 (tar bzipped)
  • compress (.Z)

Since ZIP is one of the most common formats, OS X makes it extremely easy to create a ZIP archive that contains any file or files. Simply select the file(s) and choose Create archive of... from the contextual menu:

Unfortunately, this is essentially the extent of OS X's ZIP abilities. For example, once a ZIP archive is created, you cannot add additional files to it — instead, you'll need to delete the archive and create a new one from scratch that contains the additional files. OS X also lacks the ability to create or decompress encrypted ZIP files:

compression_error_osx.gif

Aside from the above compression formats, OS X also has its own disk image format called DMG. DMGs can be created through Disk Utility in the Utilities folder. Specify a certain filesize and Disk Utility will create and mount an image of that size, allowing you to add files as you would any disk. You can then convert the image to a compressed format. Alternatively, you can create a disk image from a folder and save it as a compressed disk image. Disk Utility also allows for the encryption of disk images using AES-128 encryption.

Disk Utility can also be used to create Internet-enabled disk images, which greatly simplify the process of downloading software from the Internet. Such images will automatically uncompress themselves (when downloaded via Safari) and throw away their original compressed file, saving the user the trouble of having to do so manually.

Windows XP

XP takes the unique approach of treating ZIP archives as if they were just another folder in the file system. When you double-click a ZIP archive in XP, you can browse its contents in a regular Windows Explorer window.

To actually decompress the ZIP archive, right-click and choose "Extract All" from its contextual menu. This will open the "Compressed (zipped) Folders Extraction Wizard," which allows you to choose a location to extract the contents of the ZIP archive to (it defaults to the directory it is currently located in). It will also prompt you to enter a password if the .ZIP archive is encrypted.

To compress a selection of files and/or folders in XP, first select the files, right-click, and then go to Send To > "Send To Compressed (zipped) Folder". You can continue to add additional files your compressed folder even after you have created it. Just drag files on to it as if you were adding files to a regular folder.

Although it's not immediately obvious, you can also add a password-protect compressed .zip files:

  • Double-click on the compressed .zip file to browse its contents in Windows Explorer
  • Choose File > Add Password from Windows Explorer's menu bar.

XP has another method of compressing files on your system for the purpose of saving disk space. From a file or folder's contextual menu, select Properties > Advanced > Compress Contents to Save Disk Space. Files are compressed automatically, and will be denoted as such with a blue color. Files will decompress on-the-fly when you open them.

Conclusion

Mac OS X

  • Support for a large range of compression formats
  • Supports creation of disk images
  • Can't browse contents of archived ZIP files without decompressing them
  • No ability to create or open encrypted archived ZIP files
  • Can't add files to an existing ZIP archive

Windows XP

  • Browse the contents of ZIP files as if they were a regular folder, without decompressing them
  • Supports creating and opening encrypted ZIP files
  • Can add files to an existing ZIP archive
  • Automatically compress files/folders to save disk space

Windows XP is considerably more powerful than Mac OS X in this area. OS X users can create and open ZIP files, but that is the extent of what the operating system can do out-of-the-box. In addition to these basic abilities, Windows XP users can browse the contents of ZIP files without first decompressing them, password-protect ZIP files they create, and configure specific files/folders to automatically compress and decompress on-the-fly so that disk space can be saved.

Mac OS X: 5
Windows XP: 9

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