(The original Rosetta was released in 2006 to facilitate Apple’s transition from PowerPC to Intel. Developers won’t need to make any changes to their old apps they’ll just work. Rosetta 2 essentially “translates” instructions that were written for Intel processors into commands that Apple’s chips can understand.

That’s where Rosetta 2 comes in: It’s an emulator built into macOS Big Sur that will enable ARM Macs to run old Intel apps. But it also means that apps that were developed for Intel’s architecture originally won’t run natively on Apple’s upcoming hardware. That’s an exciting move, because it means that they’ll be able to run iOS and iPadOS apps alongside those made for macOS. The new Macs will use arm64, the same CPU architecture that recent iOS devices use (Intel-based Macs use an architecture called x86-64). The first Mac with Apple silicon is coming by the end of 2020, but Apple expects the full transition process to take two years. Earlier this week, on what Tim Cook called a “historic day,” Apple announced that it’s moving Macs away from Intel processors to its own silicon chips.

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