2/11 - Apple currently markets both IBM PowerPC G5 iMacs and Intel Core Duo iMacs, both with similar configurations. This duality affords a rare opportunity to compare IBM and Intel processors. "Thankfully, Apple has two iMacs, one based on the Core Duo and one based on the G5, that are virtually identical, thus facilitating our comparison".

First off, the G5 is a great competitor. By disabling one of Core Duo's cores, one can compare the performance of the two processor architectures. The G5 actually bests the Core Duo in most tests, with one of Intel's cores disabled.

Nevertheless, Core Duo taken as a whole manages to overall significantly outperform the G5. This is a legitimate victory, even if Core Duo has the "unfair" advantage of having two cores. A "pair of G5s could never make it into an iMac of this form factor, meaning that the Core Duo's dual core performance advantages are reasonable to flaunt".

Intel began preaching the virtues of performance per watt (ppw) at the last Intel Developer Forum. There must be something to the metric, because Steve Jobs at the 2005 WWDC said that performance per watt was one of the main reasons that Apple would switch to Intel processors. "The idea was that IBM couldn't deliver the performance per watt that Intel could over the coming years".

One of the first indicators that the new iMacs are power efficient is that they are very quiet, even under full load or system startup. Video encoding especially stresses a processor. One prominent analyst noted: "I never once heard the iMac Core Duo's fan spin up, not even during my CPU intensive H.264 encoding tests".

Benchmarks bear out the power efficiency of the processor.

If we look at power consumption by itself—apart from ppw—Intel's processor uses about 2/3 of the power of the G5. The G5 is no slouch, "but the Core Duo is in a completely different league".

Turning to ppw, the story gets even better. "The Core Duo based iMac offers about 90% higher performance per watt".

Intel's smaller manufacturing process technology works to its advantage when using the ppw metric. This is illustrated in the G5 / Core Duo comparison. Intel uses a 65nm process technology, while IBM uses a 90nm. "Intel's performance-per-watt advantage would be severely diminished if we were comparing to a 65nm G5 processor".

For the most part, Core Duo outperforms the G5 because Core Duo has two cores, whereas the G5 only has one. For example, one of the G5's strongest features is its floating point performance. Nevertheless, in an encoding test that makes heavy use of floating point, Core Duo bests G5 with a time that is three-fourths that of the G5. Why is this? Because Core Duo uses two cores, and the application is multithreaded. "The iMac G5 is pretty strong at floating point performance ... so the fact that the Core Duo completed the 304MB encoding task in 3/4 of the time set off some alarms".

One current drawback to the Intel iMac is sparse third party application support. Most Apple apps are written for the G5, not Core Duo. As a workaround, Apple provides Rosetta translation technology to recompile PowerPC code to x86. It works. But it also comes with a stiff performance penalty, and memory requirements go way up. So, if someone is heavily dependent on Microsoft Office, or Adobe, or another non-Universal application, an Intel iMac may not be the way to go.

As impressive as the dual-core iMacs are from performance, power, and ppw perspectives, there's still room for improvement and even greater innovation. The Intel iMacs use standard voltage. However, both Low Voltage and Ultra Low Voltage processors are available. This could make for Macs in smaller form factors, with even sleeker designs.