Java applications that don't rely on [[JNI]], [[Dashboard (software)|Dashboard]] [[Widgets]], and [[Scripting programming language|scripts]] that execute inside an [[Interpreter (computing)|interpreter]] all work immediately on both processors and are immune from changes. OS X applications that can't be migrated run inside a PowerPC [[Binary translation|dynamic translator]] on Intel called "'[[Rosetta (software)|Rosetta]]'." This has limitations (the biggestmost significant being that it can't run [[PowerPC G4|G4]] [[AltiVec]] code), but most applications that use AltiVec fall back to a [[PowerPC G3|G3]] instruction set when AltiVec is not found, and will still run in that configuration under Rosetta. Rosetta is a largeprocessor improvementemulator overcomparable to the 68K emulator that allows PowerPC Macintoshes to run pre-PowerPC code, rather than a virtual system like [[Classic (Mac OS X)|Classic]] since; it doesn'tdoes not require a wholesecond OSoperating system to be loaded as a subsystem before the application can work.
AltiVec itself has been encapsulated since [[Mac OS X v10.3|Mac OS 10.3]] by a vectorisation library; this library automatically selects between AltiVec on the PowerPC and [[SSE]] (or equivalent regular instructions) on x86.
A new version of [[Xcode]] has been released that supports the generation of Universal (previously called "[[Fat binary|Fat]]") Binaries for Intel and PowerPC, the new system's equivalent of the earlier 68K-PowerPC [[fat binary|fat binaries]]. [[Cocoa (API)|Cocoa]] applications can be ported simply by recompiling them and checking for endian problems. [[Carbon (API)|Carbon]] applications may require some additional tuning, but not of the complexity of the transition from Mac OS 9. Applications written using [[Metrowerks]]' [[CodeWarrior]] suite will need to be moved to Xcode.
[[Classic (Mac OS X)|Classic]] will not be supported on the x86 architecture. This means that older pre-Mac OS X software will not be able to run, to which some users running older applications (such as [[QuarkXPress]] 4 and 5) have objected to.
