The .hqx extension is used for files that are BinHex encoded for compression. They will automatically decompress when downloaded on a Mac. User-to-user transmission is usually done with uncompressed files or if the sender has Stuffit (the most common compression utility for Macs), a stuffed version is sent, usually with the .sit extension added. Macs, as a rule, do not use extensions to identify files, except where certain applications (such as Word, Excel, etc.) have standardized their use. File types are encoded in the file header along with a creater code which links a data file to the application that created it. This linkage allows you to double-click on a data file and have the appropriate application automatically open to work with it.

An application will generally not carry any extension at all. For example, Microsoft Word is named just that, no .exe or anything. The extension thing grew out of DOS naming conventions, where you were limited to an 8.3 format (8 characters, a period, then a 3-character extension). Of course, with the growth of the Internet, other extensions have proliferated, such as .gif, .jpg, .htm, etc. These are mostly to allow browsers to correctly interpret the different types of files.

You might send your Dad a .jpg (picture) file, a .doc (if he has MS Word), a .rtf (Rich Text Format, a sort of lingua franca for word processors), and/or maybe a .pdf (portable document format - Adobe Acrobat format, a great way to exchange documents between platforms) as examples of what is possible.

I hope this helps to clear some things up. Thinking this hard on a Friday morning isn't easy. Let me know if you have any more questions. It won't surprise me; I'm sure I haven't explained everything clearly.

jeffp