Inside the Machine

Chapter 10. The G5: IBM's PowerPC 970

The last PowerPC processor to succeed the Motorola 74xx family as the heart of Apple’s workstation line is the IBM PowerPC 970—the processor in Apple’s G5 computer. This chapter takes an in-depth look at this processor, comparing it to Motorola’s 7455 and, where appropriate, Intel’s Pentium 4.

I’ll begin by taking a look at the 970’s overall design philosophy, and then I’ll step through the stages of the 970’s pipeline, much as we did in the previous two chapters on the Pentium 4 and G4e. Then we’ll talk about instruction fetching, decoding, dispatching, issuing, execution, and completion, and we’ll end with a look at the 970’s back end.

At the outset, I should note that one of the most significant features ...