Because of overheating problems with the Xbox 360 Microsoft has added a 2nd heatsink.
Microsoft installs the second heatpipe heatsink to provide additional cooling for the Xenos GPU.

some xbox360 launched before 2007.8,there wasn't this heat sink,So always lead to system halted,because the temperature can't down by Cooling FAN and intrinsic heat sink

This heat sink can down the temperature around 10 degree.