NCSA Mosaic for the Macintosh User Guide: MIME Types and External Viewers


MIME (Multipurpose Internet Mail Extensions) is a format originally designed to include images, sounds, animations and other types of documents within Internet mail messages. The World Wide Web borrows this infrastructure to specify a file's type as it is transferred from a server to NCSA Mosaic.

A MIME type is in the format: type/subtype

The World Wide Web uses six major types--text, image, audio, video, and application. (There are two other types--multipart and message--that aren't currently used.) The subtype specifies the particular format of a file. For example, the MIME type of an HTML file is text/html and the MIME type of GIF files is image/gif. The meaning of MIME types with x- subtypes is undefined. x- subtypes may have different meanings in different clients.

For file formats not directly supported by NCSA Mosaic, external viewers must be obtained and set up on your system. This appendix lists some of the programs available. These freeware and shareware programs are available via anonymous FTP from,, or one of their mirror sites.

This is not a complete listing and does not include commercial programs. NCSA does not provide any support for these programs. If you have questions or problems with any of these programs, please consult the documentation that accompanies the software and/or contact the software vendors.