As we know the integrated Intel HD4000 comes with 512Mb and the dedicated graphic card nVidia 650M with 1Gb on the rMBP, I'd like to know if rMBP shares this memory to sum up a total of 1.5Gb of VRAM for both graphic devices, if not how the rMBP can switch from one to the other graphic device without even flickering?, I mean if you're using the HD4000 and then MacOSX needs more power and switch to the nVidia, does MacOSX move all the data from one VRAM to the other and viceversa?