I saw this distinction between conventional and AJAX applications at the ferris research web site. Its quite simple and good. I have reformatted it for this blog. The original author is Richi Jennings
Conventional: Display intelligence runs in the web server, which generates HTML pages to be displayed in the browser
AJAX: Display intelligence runs in the browser, which exchanges the underlying data in XML
Conventional: Page-based user interface paradigm, unlike most desktop applications; each change requires a complete new page to be transferred and displayed
AJAX: User interface design can be much more familiar — similar to desktop applications; changes can simply modify an existing object on the page and usually do not require a server transaction
Conventional: Mouse interactions are limited to clicks, which take considerable time to transfer to the server and be acted upon
AJAX: Interactions can be far richer, including dragging
Conventional: Users must wait for each interaction to complete
AJAX: Data transfers can be scheduled in the background, meaning that users don’t need to wait; data can be pre-fetched in anticipation
Conventional:Must be online to use
AJAX: Could work offline
Source: Ferris research web site
