File Formats
Mac Tip #119/17-Sept-2003

Some files you download are compressed and maybe encoded to ensure they travel more easily and more quickly via the Internet. If you receive such a file then you need to uncompress and maybe decode the file before you can install the software.

If your web browser doesn’t handle that for you automatically how do you know what to do? Here are some guidelines.

In order to help a file travel via the Internet it may be encoded. The most common encoding for Mac files is called BinHex and you will recognise it by the .hqx suffix, for example, AEC.sit.hqx.

[Update 2009: these days .zip and .dmg are much more common. Mac OS X knows how to handle most common formats for compressed files.]

That file is a 38Kb download for Mac OS 9. It’s really called Apple Error Codes 98 — System and Sad Mac error codes explained by Rustle Laidman.

If you download this file you’ll need to use Stuffit Expander to unencode it. That will create a second, compressed file called AEC.sit. So now you’ll have two icons on your desktop. You can trash the one with the .hqx suffix.

Stuffit Expander is installed on all new Macs.

Now you need to use Stuffit Expander to uncompress the .sit file. Once you’ve done that you’ll have a file called Apple Error Codes ’98 (the real thing) and the one with the .sit suffix.

You can trash the one with the .sit suffix as you no longer need it. Other compression suffixes you may see are .zip and .gz. Again, Stuffit Expander should uncompress these, though you may find you also need DropStuff installed.

Files you download may have the suffixes .smi or .dmg. These are disk image files which means they are pretending to be floppy disks or similar. With these you simply double-click the file and an icon of a drive will appear on the desktop. Double click that to open it and follow whatever instructions are contained inside it. When you’ve finished eject it by clicking on it once and choosing Eject from the correct menu in the menu bar.