With Apple's recent release of Mac OS 10.7 Lion, many users have been surprised to find, on top of many new and exciting features such as Resume, Versions, and Mission Control, that some of their favorite programs can no longer run. Apple's decision to remove support for older PPC programs has been a cause for concern for users unwilling or unable to upgrade their programs to newer compatible versions.
This problem began in 2006, when Apple began producing computers with Intel processors. For ten years prior, all Mac computers had been powered by Motorola/IBM processors called PowerPC, abbreviated as PPC. When Apple switched from using PPC processors to Intel processors, the programs written to run on PPC processors could no longer run on Intel without substantial rewriting of the programs themselves.
To work around this problem, Apple invested substantially in a technology called Rosetta. Rosetta was developed and licensed by Apple from Transitive Corporation, which specialized in transcoding programs. This Rosetta software, included in the Mac OS after 2006, allowed programs written for PPC to operate on Apple's newer processors, albeit more slowly than before. Many software developers released updates to their programs allowing them to run "natively" on the Intel processors. However, many programs were never upgraded to native Intel compatibility, and many other developers charged a substantial fee to upgrade their software to the latest compatible version.
Skip back to this past July, when Mac OS Lion was released. This version of the Mac OS no longer contained the Rosetta software, resulting in many older PPC programs being unable to function on the Intel processors Apple had been using for the last five years. This had been Apple's strategy since the introduction of Intel-powered computers in 2006, to unify both the programming language and platform for which programs were written on Mac computers. While this may have simplified the development of new programs being written for Macs, it has left the substantial library of older programs without the ability to function on Apple's latest supported operating system.
The solutions to this are few and far between. Apple has suggested either upgrading programs where possible and available, finding an equivalent Lion-compatable program, or finding a Windows version of the same program to run under Boot Camp by installing Windows or a Windows virtualization program such as Parallels Desktop or VM Ware. None of these options are the simple, easy-to-use "it just works" solution users of Macs have come to expect over the last few decades, leaving users out in the cold. Transitive Corporation, the company whose software upon which Rosetta was based, has indicated to the press that it is open to developing solutions for individual software developers to make their programs compatible with Mac OS Lion, but this solution may be both cost-prohibitive and too slow to see mass adoption.
So for those users who are upset that their new Mac OS Lion can't run their favorite older PPC programs, the only solution at this point is to follow one of Apple's suggestions. This sacrifice of computability for unity and stability is one which Apple has made, and the rest of us must simply live with.