Apple's refresh of the iMac line today no doubt left some rival manufacturers scratching their heads over how Steve Jobs and Co. got early access to the X9100 3.06GHz Centrino 2 chipset. Not scheduled to be launched until June, the CPU - aka Montevina - will have a 1,066MHz front-side bus, compared to Santa Rosa's 800Hz. Turns out, the answer is that Apple didn't get priority access; instead, Intel have tweaked an existing-generation CPU especially for the iMac.
Matching Montevina's core clock rate and FSB, the chipset is in fact overclocked to 3.06GHz with special support for the 1,066MHz bus. Until now, Intel's models in the range had peaked at 2.8GHz. The cost is increased power demand: whereas current chipsets draw a maximum of 45 watts, the iMac-special requires 55 watts. The mainboard uses the same Santa Rosa chipset as the other iMacs.
The resulting extra heat, together with the excessive draw from a laptop battery, is what made the chip unsuitable for mobile use. Intel's Centrino 2 platform is expected to require a mere 25 to 35 watts when they launch.