What's the average number of PCB layers used for laptop mainboards?

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I've heard that laptop mobos tend to use more layers to provide better EMI/RFI insulation. I'm particularly interested in the number of layers used on the IBM T40 series. Many thanks.

 

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*bump*

 

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FYI: I did a little digging myself on Intel's i855PM design guidelines and the answer to my question is 8.