What is difference in video performance between streaming and progressive download?

When you store your video files on a conventional Web server and the files are downloaded through HTTP, then we are talking about “Progressive Download”. Progressive (HTTP) download is the most common method for transferring files over the Internet: when you visit a Web site, all of its elements, text and images, are transferred in this way.

Contrary to Progressive Download, Streaming is accomplished through specialized Media Servers which are optimized for transferring digital video/audio. The transference is managed by messages that are sent/received between the WebTV (Video Player) and the Media Server.