My question is: is OSM usinig raster or vector transfer type? By raster tranfer I mean that showing map on our screens is done by OSM servers and then tranffered in the www. If you zoom the server will create new look and tranfer it again to our screen in www. While vector tranfer do not create internet traffic. I mean that once it download all the vector, you can do all the operations using the vectors. It doesn’t go with any net traffic. It may need time on the beginig to download data, and alsa may need some software or hardware minimums to proccess the operations. Can anyone answer the question? 
OSM is simply the database with all the data in xml-vector format.
Everything else is up to the renderers. You are right, that the renderer Mapnik for our “main” map is transfering
.png tiles (raster-format).