Apple transitioned to Apple Silicon starting in 2020, replacing the Intel CPUs transitioned to from PowerPC 2006. This book was written during Apple’s first transition: from Motorola 68K to PowerPC in 1994. Why the heck would I read a book from 1994 about a microprocessor that’s now two transitions defunct? History!
I love history and understanding how things evolve to where they are today. While all of Apple’s processor transitions started for the same reasons (performance, power usage), they each proceeded differently. Contemporary 68k applications were run through emulation, similar in concept to Rosetta and Rosetta 2, but the Mac OS was run through this emulation as well. At that time, Apple couldn’t simply recompile Mac OS for PowerPC because too much of it was written in 68k assembly. Add to that additional assembly in MacOS applications as well as very little hardware abstraction, and it was very time consuming to port applications fully to PowerPC.
The result was that parts of Mac OS and its applications ran under emulation for more than half a decade. This emulation was provided initially through the ROM chip in PowerPC macs until it transitioned to software ROMs in the iMac. Apple continued to increase the PowerPC nativeness of the MacOS over the years, promising a full native OS with the failed Copland project, and only delivering it with the release of the NeXT-based Mac OS X in 2001. By this time Apple and developers could largely recompile their code for future processor architectures, which made Rosetta and Rosetta 2 possible.
The book is full of interesting details about Apple’s pre-PowerPC experiments with RISC architectures, how the Apple IBM Motorola alliance came together, how the 68K emulator works, how it was delivered so quickly, and why it didn’t always make sense to “go native”. It includes technical details of the PowerPC 601, 603, 603e, and 604 CPUs; and details how emulated and native code interact within System 7. I found its 200+ pages fascinating.
Verdict: Don’t read unless you are a nerd like me.
Relatively Ambitious 