Lightroom utilizes all four cores in the PC world, give it loads of RAW's to convert and then take a look at performance under the task manager, all 4 get hit almost equally.
Also Lightroom can do more than one job at once, so you can leav it rendering previews whilst you quickly process 20 shots for a website, it will run them plus two more jobs at the same time and really hammer your CPU's cores, your cached physical memory and the speed of your hard drive link.
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