NCSA Mosaic for MS Windows User Guide: External Viewers


MIME Types Explained
Most of the files you find while exploring the World Wide Web are MIME typed. The MIME (Multipurpose Internet Mail Extension) type defines the type of file. For example, plain text, HTML, image, movie, and audio files are specific file types that correspond to a specific MIME type.
Mosaic uses MIME types to determine what it needs to do to display the file. A MIME type is constructed of two parts: the main type and a subtype. MIME types are represented by writing the main and the sub parts together and separating the parts with a forward slash (/), such as text/html.
Even though Mosaic is capable of reaching the far corners of the Internet, it's only capable of displaying a few MIME types:
- text/plain (ASCII text files)
- text/html (files containing HTML codes in addition to ASCII text)
- image/gif (image files in .gif format)
- image/xbm (image files in X bitmapped format)
When Mosaic encounters a MIME type that it can not directly display, it does one of the following:
- sends the file to a defined application that can display the file
- saves the file to disk
- associates the file with an application
- cancels the file transfer
External applications work with Mosaic to display just about any file on the Web. Mosaic downloads the file, determines what external applications software is needed to display the file contents, and then opens that applications software. These external applications are called external viewers.
Mosaic doesn't care which external viewer you use to view a file type as long as the software accepts command line inputs. (Most applications can accept command line inputs, but if you have questions, contact the developer.)
The list of current MIME types can be found at:
ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/media-types

