Inside the Machine

The PowerPC 970's Back End

The PowerPC 970 sports a total of 12 execution units, depending on how you count them. Even a more conservative count that lumps together the three SIMD integer and floating-point units and doesn’t count the branch execution unit would still give nine execution units.

In the following three sections, I’ll discuss each of the 970’s execution units, comparing them to the analogous units on the G4e, and in some cases the Pentium 4. As the discussion develops, keep in mind that a simple comparison of the types and numbers of execution units for each of the three processors is not at all adequate to the task of sorting out the real differences between the processors. Rather, there are complicating factors that make comparisons ...