Rosetta

Rosetta (retroactively referred to as Rosetta 1) is a lightweight emulator for Mac OS X distributed by Apple. It is based on Transitive Corporation's QuickTransit technology and enables applications compiled for the PowerPC family of processors to run on Apple systems that use Intel processors. It was introduced in 2005 as a key part of Apple's strategy for the transition of their Macintosh line from PowerPC to Intel processors, allowing pre-existing Mac OS X software to run on the new platform without modification. The name is a reference to the, whose discovery made it possible to comprehend and translate Egyptian hieroglyphs. Rosetta 1 was phased out by Apple in 2011 and reintroduced as Rosetta 2 in 2020 to support the transition from Intel to Apple processors.

Features
Rosetta is included, pre-installed with the operating system, on Macintosh computers that use Intel's Core processors. It translates G3, G4, AltiVec, and OpenGL instructions, but it does not translate software that requires the G5-specific features of later Apple systems; such applications have to be modified by their developers to work on Intel-based Macintoshes. However, there are very few applications that strictly require the G5 processor, so compatibility with most applications is possible.

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 or Photoshop) are not. Pre-existing PowerPC versions of Apple "Pro" media-production applications (such as Final Cut Pro/Express, Motion, Soundtrack Pro, DVD Studio Pro, Aperture, and Logic Pro/Express) are not supported by Rosetta, and require a "crossgrade" to a universal binary version to work on Intel-based Macs.

In general, Rosetta does not run the following:
 * Applications built for Mac OS 9.2.2 or earlier.
 * Code that inserts preferences into the System Preferences pane.
 * Applications that specifically require a PowerPC G5 processor.
 * Kernel extensions, and applications that depend on them.
 * Software that requires a specific legacy hardware interface to operate (see kernel extensions above)
 * Bundled Java applications or Java applications with libraries that can’t be translated.
 * Java applets in Rosetta-translated applications. That means a PowerPC-only web browser application (such as Microsoft's legacy Internet Explorer for Mac) will not be able to load Java applets; an Intel-ready version of the browser is needed (such as Safari, Camino, or Firefox).

History
Rosetta first appeared in October 2005 as part of Mac OS X 10.4.3 to support Intel-based Macs. Rosetta became an optional download for Mac OS X 10.6, and was no longer supported by Mac OS X 10.7.

Rosetta 2 was announced on June 22 at the 2020 Worldwide Developers Conference. This new version, introduced as part of MacOS Big Sur, allows Intel software to run in emulation on Apple processors.

Other uses of the name

 * Rosetta was also the internal codename of the CalliGrapher handwriting recognition engine licensed and adapted by Apple for use in Newton OS.