Rosetta (software) – Wikipedia, the free encyclopedia

Rosetta is a lightweight dynamic translator for Mac OS X distributed by Apple. It enables applications compiled for the PowerPC family of processors to run on Apple systems that use Intel processors. Rosetta is based on Transitive Corporation’s QuickTransit technology,[1] and is a key part of Apple’s strategy for the transition of their Macintosh line from PowerPC to Intel processors as it enables pre-existing Mac OS X software to run on the new platform without modification. …

Rosetta is part of the Mac OS X for Intel operating system. It translates G3, G4, and AltiVec instructions; however, it does not translate G5 instructions. Therefore, applications that rely on G5-specific instruction sets must be modified by their developers to work on Intel-based Macs. According to Apple, applications with heavy user interaction but low computational needs (such as word processors) are well suited to translation via Rosetta, while applications with high computational needs (such as raytracers or Adobe Photoshop) are not.  …

So in like 2005/2006 they thought, Intel Macs would not be sufficiently fast to execute software with “high computational needs” through Rosetta, but >2010 Intel Macs are powerful enough to do even that. Somebody told, his old PPC Mac Photoshop runs nicely on his 2010 Snow Leopard MacBook Pro, and he was very delighted about that.