Chromatix wrote:
Because both the 68K and PowerPC were big-endian, it was relatively straightforward to write an emulation layer that allowed existing 68K Mac software - including, initially, much of the operating system! - to run on the new PowerMacs, often actually faster than on a native 68K CPU. That allowed Apple to legitimately claim a high degree of backwards compatibility, despite the two CPU architectures being very different. The fact that an 80MHz PowerPC would run native software about 5x the speed of the 40MHz 68040 (from just the previous year) showed clearly the advantage of migrating.
This is apposite too: the ARM ran a
very efficient 6502 emulator, allowing for Acorn's Archimedes range to have some binary compatibility with applications built for the 6502-based BBC Micro. Indeed,
one of the Archimedes range was branded as a BBC machine, somewhat later. (There was also a degree of compatibility in the Archimedes running BBC Basic, in a version fairly compatible with previous versions running on 6502 (and on other platforms.))
Today, we can run an emulated 6502 on ARM, specifically on Raspberry Pi, which does
a very good job of acting as a minuscule but very fast second processor to Acorn's original 6502 line.