Now, I have something to tell you today. Mac OS X has been leading a secret double life — for the past five years. There have been rumors to this effect... but this is Apple's campus in Cupertino — let's zoom in on it — in that building right there... we've had teams doing the "just-in-case" scenario; and our rules have been that our designs for OS X must be processor independent, and that every project must be built for both the Power PC and Intel processors. And so today for the first time, I can confirm the rumors that every release of OS X has been compiled for both Power PC and Intel — this has been going on for the last five years. Just in case.

2005-09 - WWDC 2005