" In addition to an older version with the GK107 chip (384 shader, 810 - 895 MHz, 128 bit memory), there also exist models with the new GK208 (384 shader, up to 980 MHz plus boost, 64 bit memory). Both versions usually use DDR3 memory; however, GDDR5 versions are possible, too."
Tehát a régi GK107 chip-es 740M 128bites, az új GK208 chip-es 64bites.