When you link a narration, the file size of the presentation is smaller, because the sound file is stored outside the presentation. You specify a location on your hard disk drive for the narration, and the sound file plays with the presentation. If you give the presentation on a different computer, you must move the linked sound file to that computer. The best way to move a presentation and its linked files is to use the Package for CD feature. Or you can manually update the links on the second computer by deleting the narration and then adding back the narration sound file before you deliver your presentation.