A universal Mac application will work on both newer Macs using Intel CPU chips, and older Macs running PowerPC CPU chips. If an application is not universal, it may not run on all Macs, although some Intel Macs can run PowerPC applications if they use Mac OS X 10.6 or earlier.
PowerPC vs. Intel
Apple used PowerPC chips for all Macs from the mid-1990s until the mid-2000s, and began switching to Intel chips in 2005. Older PowerPC-only applications need translation software, called Rosetta, to run on Intel hardware. However, Apple dropped Rosetta from Mac OS X starting in 10.7. Intel applications cannot run at all on PowerPC Macs.
In contrast, a universal Mac application is one that can run on both PowerPC and Intel Macs. This is determined by the author of the application, and is not always possible, depending on what features are included in the software. Universal applications were very common during the transition from PowerPC to Intel, but newer Applications written for Mac OS X 10.7 and later are Intel-only.
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