Apple did this the very first time in the early 1990s, with the move from Motorola 68000 (a.k.a. 68K) to PowerPC. Motorola’s 68K chips were losing steam, and in order to keep up with IBM PC compatibles running Intel processors, Apple got together with Motorola and IBM to define a new processor architecture, the PowerPC. In order to make this move while still supporting all of the Mac’s existing software, including its operating system, Apple needed to create an emulator for 68K instructors that would run on the PowerPC. This was a multi-year project, which was started by engineer Gary Davidian at Apple in the middle of 1990….
Davidian’s emulator served as a proof of concept that emulation of 68K code could be done without too big of a hit in software speed. This convinced managers at Apple that emulation was a workable solution for users…. In October 1991, Apple announced the PowerPC alliance with IBM and Motorola, and work began to shift Davidian’s emulator over to the PowerPC architecture. New prototype plug-in boards and then full machines were built with the new chip, whose bugs were still being worked out. It took several more years, until 1994, for the first Macs with PowerPC processors, the Power Macintosh 6100, 7100, and 8100, to be released to customers. The PowerPC would be the Mac’s CPU until 2006, when Apple replaced it with Intel’s processors.
The CHM article links to a couple of its oral-history interviews with Davidian. Nobody thinks about the PowerPC transition much now, but it set the bar for Mac chip transitions. Rosetta 2, coming this fall to Apple silicon Macs near you, is the inheritor of Davidian’s legacy.