So.. The xbox 360 has 2 frame buffers, each of which renders video at 1152x640. A framebuffer holds the color value of every pixel to be displayed. Normally, the 360 would take values from each buffer and merge them together to create a higher resolution image (Though, assuming these ARE the actual maximums for the frame buffer, the xbox 360 can only really do a native 1920x768 (Or 1280x1152; 1474560 pixels max) image.... 1920x1080 has some made up data somewhere; 720p fits.) Halo 3 uses each framebuffer INDEPENDENTLY to store high dynamic range lighting values in one and low dynamic range lighting values in the other, presumably averaging the two values for each pixel address space to get a final output value for the screen. Why in the hell they don't calculate this average BEFORE putting the values into the framebuffer (Thus allowing maximum resolution) is beyond me, but presumably it has to do with performance (And that really comes down to poor optimization (more likely), or the fact that they're rendering so many damn polygons on the screen at a given time (particularly in wide open spaces. Either way though, bungie is really just being lazy and relying on the fact that the 360 has a REALLY good hardware scaler (ANA, HANA for the HDMI consoles) that scales in very high quality to almost any resolution without taxing the GPU/CPU at all.