As Thorazine said. Also, 64Bits means that all math operations are done almost twice as fast. If system is 64B and all apps are 64B - You will see an increase in performance using those apps. Don't measure it with benchmarks - they're very often all wrong. In Snow Leopard almost every essential system app is 64B now, including Finder, Mail, Safari, Preview, QuickTime etc. i guess only iTunes and few others are still 32B - what's actually strange cause if i remember well - there is 64B version of iTunes for Windows.

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