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Installing DiskDoubler is easy. Simply double-click on Salient’s installer application and it automatically installs the DiskDoubler files, including the application, the extension, and the help file. Reboot, and you’re on your way to freeing up much-needed disk space.

After rebooting, you’ll notice a new menu in the Finder next to Special, “DD.” DiskDoubler consists of two parts, a system extension (INIT) and an application. The extension puts up the menu and handles much of the automatic compression and expansion work. The application will also compress and expand files if you wish to do it manually, but most people will only see it when they double-click on a DiskDoubler file. Then, the application will run, expand the file, and look for the application that created the file. To start saving disk space, select one or more files or folders in the Finder, and choose Compress from the DD menu. DiskDoubler will start crunching away at the files and within a few seconds to a few minutes (for larger files), you’ll have cut the file size down by an average of 50%. As is always the case, different types of files compress differently, but DiskDoubler’s Method B is as good or better than any other of the programs’ compression schemes.

All the other features of DiskDoubler are available from the Finder menu as well. You can expand files manually rather than from within the standard file dialog box or by double-clicking on it. If you want to compress and combine the selected files, there’s a Combine command, which is useful for sending a bunch to someone else with DiskDoubler. If you have a very large file (a TidBITS Archive, for instance) you’ll need to Split the file to fit on floppies or through mailer gateways. File Info will give you some information on how well the selected file was compressed. Help, Settings, and About DD are self-explanatory, but it’s worth mentioning that DiskDoubler does support Balloon Help in its Settings dialog box, which is the only complicated part of DD to use. The numerous settings you have control over include:

  • how DiskDoubler will compress the file,
  • when it will provide feedback about what it’s doing,
  • how soon it will update the Finder information,
  • how large split files should be,
  • what it should do with combined files after expanding,
  • whether it should quit immediately when it’s done or stay on the screen so you can see how it did,
  • if it should verify files after writing,
  • if it should expand related application files (like dictionaries and preference files in the same folder as a compressed application),
  • and if it can use the DiskDoubler application to switch to the background while expanding and compressing.

Obviously, your choices in these settings can affect DiskDoubler’s real world performance significantly, but it’s easy to play with them to find your favorite combination. For instance, I don’t mind the speed hit of using the Smallest Guess option in favor of the extra savings most of the time, and I also have DiskDoubler update the Finder information immediately and verify files after writing, even though those options slow it down. However, I let DiskDoubler operate in the background, which prevents it from seeming slow even when compressing or expanding a large file if I have something else to do.

Those are DiskDoubler’s primary features, but the DD menu changes when you hold the Shift key down and also when appropriate. So, if you select one piece of a split file and drop down the DD menu, Split will change to Join. Holding down the Shift key changes Compress and Expand to Compress To… and Expand To…, both of which let you save the compressed or expanded file in a different location, which is useful on occasion. Combine will change to Create SEA… which will create a DiskDoubler self-extracting archive and let you save it where ever you want. Finally, Split changes to Copy To…, which will copy the selected files where ever you want more quickly than the Finder. I’m perhaps making it sound more complicated than it is, but I do want to give you a sense of how much DiskDoubler can do despite its simple purpose.

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