Core 2 Duo is set to launch tomorrow, July 27, 2006, and many people are wondering if the iMacs will be updated to use these chips. The timing would be right, considering the last iMac update was in January, over 6 months ago. However, let us look at the options:
1) Core Duo: This 32-bit chip is what the iMacs use now, and the upgrade path would be the next step up to Core Duo T2600 2.16 GHz. This is a viable option, but the pricing of this chip is a bit high at least for now, at $423 (in trays of 1000, although Apple would pay less).
2) Core 2 Duo Merom: Merom is a direct 64-bit replacement for Core Duo, but unfortunately the cost of these chips is comparatively high. The 2.16 GHz T7600 is slated to be $423 as well, so the cost of the T7600 also may be undesirable. While the 2.0 GHz T7200 is only $294, and Merom Core 2 Duo is clock-for-clock faster than Yonah Core Duo, the 2.0 GHz Merom wouldn't be ideal from a marketing point of view since the current Core Duo is already 2.0 GHz.
3) Core 2 Duo Conroe: This 64-bit desktop chip based off Merom is a strong possibility from a marketing point of view. Apple could launch the iMac with the new Core 2 Duo E6600, a 2.4 GHz chip with 4 MB L2 cache. That's quite a clock-speed and performance boost for the iMac, but with a chip price of only $316.
The one issue of concern with Core 2 Duo Conroe is its TDP of 65 Watts. This is considerably higher than the 31 Watt TDP of the current Core Duo, and likely also higher than the G5's max power in the last PowerPC iMacs. However, the last PowerPC iMacs were not all that cool either, considering the G5 970FX's max power utilization at 2.0 GHz and 2.2 GHz was 50 and 60 Watts respectively, and the last PowerPC iMac was at 2.1 GHz. While TDP cannot be directly compared to IBM's max power specs, it is likely in the same general ballpark, which suggests that the iMac can easily handle chips over 50 Watts. Given my experience with my own 2.0 GHz iMac, it's clear that the machine is built to handle something even hotter, since the machine doesn't get that loud even at full tilt. Along with the fact that dual-core Intel CPU has superior power saving features and that it would need less of its CPU to support basic usage, that would mean that an iMac with such a chip would still be quiet with normal daily computing.
Thus, I think it's likely that the next iMac will use Core 2 Duo Conroe, probably at around 2.4 GHz. The venue for its release may be WWDC next month, alongside new quad (dual dual-core) Intel Xeon Woodcrest Mac Pro towers.