Hypermedia generalizes the notion of hypertext to include sound and interactive video in documents. For example, a document on Mozart could include portions of his music which readers could listen to simply by clicking the mouse on a link in the main document. Several publishers have begun to produce hypermedia versions of their products. For example, there is a version of Grolier's Encyclopedia available on CD ROM that has sound and movie clips included with the text. If you read about US presidents, you will see pictures of the presidents. Some of these pictures have links that will play a movie (complete with sound) showing part of that president's inaugural address.
Mosaic and Netscape are hypermedia browsers for Unix platforms, Macintoshes and PCs. They display information in a window and use keystrokes and mouse clicks to navigate through the document. Documents can be read as normal text files by using a scroll bar and mouse buttons to move back and forth in the text. Clicking the mouse on a link will either move you to another location within the current document or call up a new document. If necessary, the browsers will use the Internet to fetch a document when you select it; for example, if you are viewing a document on an art exhibit that has a link that refers to a particular piece, when you click the mouse over the link the browser will invoke FTP to copy the image and then invoke xv to display it in another window. It is the ability to call external software (such as FTP and xv) that makes these browsers hypermedia software packages: if you select a movie or piece of music, Netscape or Mosaic will invoke software to play the movie or sound.