NCSA Mosaic for the Macintosh User Guide: Customizing

Helper Applications

MIME Explained

How does Mosaic know that a GIF file is a GIF file and not a QuickTime movie or a plain text file?

Usually, the server tells Mosaic the MIME type of the file it is sending. Originally, MIME--Multipurpose Internet Mail Extensions--was just a method of including images, sounds and other non-text information in a mail message. MIME has now been incorporated into other systems such as the World Wide Web. See "MIME" on page C-1 for more information.

Based on a file's MIME type, Mosaic knows whether to handle the file itself (i.e., if it is an HTML file) or to pass it off to an external viewer.

Some servers--such as FTP servers--do not use MIME types. In that case, Mosaic tries to infer the MIME type from the file extension. For example, a file ending in .gif is assumed to be a GIF file; one that ends in .html is assumed to be an HTML file.

You are able to modify the MIME types in the following ways:

Obtaining Software

A list of software and where the software can be obtained is available by choosing FAQ from the Balloon (help) menu. Click on the Helper Applications hyperlink.