Compression

Mac OS X has built in tools for file compression (i.e. reducing file-size). This makes life easier if you have a large file that you wish to compress in order. say, to email to a friend.

The first way is to right-click (or Ctrl-Click) on  the file in question and select the “compress” command (OS X 10.5) or “create archive” (earlier OSs) - this will create a zip archive of the file or folder which can be opened on windows machines.

The second way is through “Disk Utility” (Macintosh HD > Utilities > Disk Utility). This fantastic software, included free with all versions of OS X, is a veritable Swiss Army Knife as it has so much functionality. Once launched, all you need to do is go to the File menu, and select “New > Disk Image from Folder” command and this allows you to create a disk image (.dmg) from any folder on your Mac. Note that your original folder remains untouched. Disk Image files can not be opened by windows machines.

If you are interested in compression, there are also a huge number of third-party utilities for file compression that do the work for you - here are some you can find at Versiontracker.