From Mac Guides
Rosetta is Apple's marketing name for a PowerPC emulator that ships with the Intel version of Mac OS X. It is licensed from Transitive Corporation, where it goes by the name of QuickTransit. Rosetta translates PowerPC binaries into Intel binaries to provide an emulation layer for applications as the Mac platform migrates to Intel.
This will allow PowerPC applications to run under the new Intel-based Macs. Therefore this technology is only of importance to users who are buying or have bought an Intel Macintosh.
At WWDC 2005, Steve Jobs demonstrated Rosetta and listed these features:
- Dynamic binary translation
- Runs existing apps
- Transparent to users
- Fast (enough)
Over time, as developers compile applications to run on both Intel and PowerPC processors, the importance of Rosetta will wane.
Rosetta will not run the following applications:
- Classic Environment, and subsequently any Mac OS 9 or earlier applications
- Screensavers written for the PowerPC
- System Preference add-ons (preference panes)
- Applications which specifically require the PowerPC G5
- Kernel extensions
- Java applications with JNI libraries
Also, Apple reports that "Final Cut Pro, Motion, Soundtrack Pro, DVD Studio Pro, Aperture, Logic Pro, Logic Express, Shake and Final Cut Express" are not supported by Rosetta.  Instead users will have to upgrade to the Universal Binary versions of their software.
To tell what processor a particular application was built for, simply choose the application in Finder and choose Get-Info from the File Menu.
- Universal means it was written for both PowerPC and Intel.
- PowerPC means it was only written for PowerPC and will use Rosetta when run on an Intel Mac.
- Intel means it was only written for Intel and will only run on an Intel Mac.
You can also use the lipo command line tool to inspect an executable, for example
QuadG5:~ shawnce$ lipo -info /Applications/iTunes.app/Contents/MacOS/iTunes Architectures in the fat file: /Applications/iTunes.app/Contents/MacOS/iTunes are: ppc i386
- ppc means the executable contains a PowerPC version of the executable.
- i386 means the executable contains a Intel (IA32) version of the exectuable.
- If you see both ppc and i386 the executable is considered Universal.
Rosetta was also the code-name for Apple's in-house handwriting recognition software for the Newton. Rosetta was also known as the Newton's "cursive" handwriting recognizer.
- Benchmarks of Rosetta on a 2.0GHz Core Duo iMac. Speeds ~30-50% 2.1GHz G5 iMac.
- Rosetta Developer Documentation from Apple
- Rosetta Info Page on Apple.com
- List of Universal Binary Applications at osx86project.org
- Transitive Corporation - the company behind the technology in Rosetta
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