Part1 Mapserver Itasca Application has architecture similar Thin client architecture is user request to web server by web browser. The web browser will render and send data to user in image map form (User cannot access raw data) such as image map in tmp folder. Part3 Open Layers KML example has architecture similar Medium client architecture is user request to web server by web browser which web browser will perform information data set and send two data to web browser (image map and KML file) for web browser will render and show to user. Therefore when disconnect internet still access data because web browser have data from render at the time (image map and KML file). And user can access raw data from web browser is KML file which it can download in to the drive. The difference between Part 1 and Part 3 is accessibility to raw data from web server.
Mapserver Itasca Application is a thin-client. We can use zoom in, zoom out, pan, query a feature. Image map shown have been done in server. Client computer display map only. Thus, sometimes it response slowly. Moreover, it is created by HTML.
Openlayers is a medium-client. We can use zoom in, zoom out, pan and get information by popup. Although Internet disable that we can see popup information because in this section is rendered in client computer. Mapserver Itasca Application cannot be able.