Birt Phases and CPU

Libramind

I read in the ROM scripting document, that there are 5 phases ( startup, Data trans., Factory, Presentation, shutdown ). Are all 5 phases consuming cpu on the server side? Do any of these processes execute within the client browser using javascript/html/etc.? I ask, because in our onDemand app, we could have a thousand users calling up reports, concurrently. If a document is built for each report on the server, it could consume excessive memory.