Quick! Switch on your 9400 and open up iStat! Look at the temps related the GPU. You will see 2: "GPU" and "GPU Heatsink" Now, go fire up your 9600, and look again. There will be 3: "GPU", "GPU Heatsink" and "GPU Diode". So, that apparently means GPU Diode is the 9600's core sensor, or at least a sensor very close to the die. The very high numbers this sensor reads would back that up. But where the heck are the other two? Let's start with the heatsink one. If quick look at the iFixit disection shows there really isn't any "GPU Heatsink". There's just a heatpipe covering the CPU, chipset, and GPU, and running to some small fins (w/fans) and to the top of the unibody (make your machine do something processor intensive, then feel the case between F3 and the screen hinge, you'll see what I mean). My best guess is that it is on the heatpipe, I really don't know. The stranger one is "GPU". This one never seems to go away, even when the 9400 is ostensibly off. Which leads me to wonder, does it ever actually turn off? And if it doesn't, is it doing any processing behind the scenes, or is it simply idling the whole time?