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I'm curious; I thought the Northbridge was under the smaller metal heat sink between the processors. What are the ICs being protected by the strip of thermal pad on the bottom of the processor heat sink?

When I recently upgraded the processors in my MP 5,1 I cleaned quite a bit of junk off of the ICs that these thermal pads protected on the processor board. The thermal pads themselves looked OK.
 
I'm curious; I thought the Northbridge was under the smaller metal heat sink between the processors. What are the ICs being protected by the strip of thermal pad on the bottom of the processor heat sink?

When I recently upgraded the processors in my MP 5,1 I cleaned quite a bit of junk off of the ICs that these thermal pads protected on the processor board. The thermal pads themselves looked OK.
Pwm/power plane.
 
So, "Pwm/power plane" is part of the power management circuitry for the processors?
It's the power circuit for the processors and DIMMs. Takes the 12V from the PSU and then changes it to the correct voltages for the processors and memory.

Power management have another meaning here.
 
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