A lot of applications generate their own data. The pure "on disk" piece might be a fraction of the total. e.g., consider z-sorting vertices for a million-polyg

A lot of applications generate their own data. The pure "on disk" piece might be a fraction of the total. e.g., consider z-sorting vertices for a million-polygon model as it rotates (that's useful for some kinds of transparency.) Bandwidth to main memory is a small piece of the total.