Aaaaaaaa, you two, you are not listening! RENDERING ITSELF DOES NOT ADD MEMORY OVERHEAD. PERIOD. You are talking about a different thing. You are talking about opening a scene. Of course your drive will swap if you try to open a 500 MB scene on a 256 MB computer. There's no space in memory for the complete scene. So when you start rendering a scene bigger than the RAM you have, computer has to load different parts of the scene one after the another. But it's not a matter of rendering, it's a matter of LOADING, because the complete scene is not in memory. Repeat, the rendering itself does not depend on memory. The calculations are always done at the same speed regardless how much memory you might have. There's no speedup in rendering if you add more RAM, there's a speedup in loading. If, for instance, we are talking about a 50 MB scene, it will render at the same speed with 256 MB RAM or with 1 GB RAM. If rendering was RAM-dependent, the computer with more RAM would render the same scene faster. It's not the case.

-- erlik