Okay, I know I'm playing with fire here so let me toss out a couple caveats. I own both a Mac and a PC and like both. This is not a debate about the OS or about which is "better" overall so please no flames. With that said....
I was reading Lloyd Chambers recent article about optimizing Lightroom for the Mac and noticed that he raised an issue about the inefficiency of his Mac Pro in utilizing all the CPU cores in his machine when doing major tasks such as importing/rendering 1:1 previews and exporting. The full article is here:http://macperformanceguide.com/Optimizing-...PerformanceTips
I had noticed previously that the activity monitor on my PC seemed to show pretty good usage of all CPU cores during import/export so it occurred to me that the PC version of Lightroom might be better optimized than the Mac version of Lightroom when it comes to efficiently using all CPU cores. To get a sense of the performance difference I replicated Lloyd's two primary tests for comparison. The test was to do the following 1) Import 128 RAW files from a 1Ds Mark III (add to catalog without moving and render 1:1 previews) and 2) Export 128 full quality JPG files from 1Ds Mark III RAW files. Lloyd's current generation Mac Pro 2.93Ghz 8 Core (dual quad core) with 32GB RAM did test 1 in 603 seconds and did test 2 in 351 seconds.
My PC running Vista Home Premium 64bit with a Q9950 Intel quad core processor at 3.6Ghz with 8GB of RAM did test 1 in 313 seconds and did test 2 in 306 seconds.
The activity monitor showed that all 4 cores on my system stayed at above 50% usage the entire operation, suggesting to me that the PC version does a much better job of using all the CPU cores. The difference in import speed was particularly surprising to me with the PC performing almost twice as fast as the Mac Pro. On the export side, the difference might be more about clock speed than CPU usage since the proportional difference is about the same. Keep in mind that we are comparing a top of the line $6k Mac Pro with a moderately quick $1k home build PC.
Is there a reason that Lightroom runs faster on the PC? Is it due to the 64bit OS? I also wonder if PC Lightroom is faster in other operations beyond just import/export, but I don't have a way to test that.