Apple has underclocked the GMA950 in the MacBook. It is clocked to run at 250MHz instead of 400MHz. Can be confirmed by an Apple TechNote Document. "Internal to the North Bridge IC is the graphics subsystem, which includes the Intel GMA950 graphics processor with 64 MB DDR2 SDRAM shared with the main memory. The internal graphics interface runs at 250 MHz." Intel's documentation shows that the it runs at 400 Mhz I suppose it's an effort to conserve battery life and to reduce heat.