>  Also, I'm wondering that nowadays there are many games with ginormous
> amounts of scenery (such as eg. Oblivion, Fallout 3 and Far Cry 2). I 
> doubt
> all that scenery would fit in RAM at once, much less in the graphics card.
> The scenery is being loaded on-the-fly as the player advances in the 
> terrain
> (in the latter two example games mentioned, this is done transparently,
> without any "loading" messages or delays). Naturally all this scenery 
> needs
> to be transferred to the GPU.

Graphics cards can store quite a lot of mesh and texture data on-board, the 
CPU algorithm just needs to carefully predict and spread out any big updates 
to avoid noticeable frame rate drops.  For example some common meshes like 
trees and grass might always be in the GPU memory, but some detailed 
versions of buildings might only be loaded when you get near to them, and 
the actual mesh load peformed over several frames.  The terrain is also 
typically sectioned up, and the LOD for each section is dtermined by a CPU 
algorithm and the GPU updated whenever necessary.  This way, *most* frames 
you will hardly be sending any data from the CPU to the GPU, and the frames 
where you do need to send mesh data you are only sending a very small amount 
that won't impact the rendering performance.

Of course if it all doesn't fit in normal CPU RAM the CPU algorithm must 
also manage reading from the disk in a similar way to be transparent.

It's certainly not trivial to implement a massive game environment.

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