Camera plane division

with how geometry and textures keep pushing the envelope of what ram, graphics card and processor can handle one of the most useful facilities I can think of at the moment would be being able to divide up a cameras frame into 2 or 4 areas which could be rendered seperately. Is there anything like this already out?
Comments
Use the Spot Render tool and, in Tool Settings, set it to render to a new window. However, don't forget that Iray will still need to load the entire scene (in order to corectly handle light bounces) so i doubt it will help much.