Inside the Machine

The PowerPC 604

At the same time the 603 was making its way toward the market, the 604 was in the works as well. The 604 was to be Apple’s high-end PPC desktop processor, so its power and transistor budgets were much higher than that of the 603. Table 6-3 summarizes the 604’s features, and a quick glance at a diagram of the 604 (see Figure 6-3) shows some obvious ways that it differs from its lower-end sibling. For example, in the front end, the length of the instruction queue has been increased by two entries. In the back end, two more integer units have been added, and the CR logical unit has been removed. These changes reflect some important differences in the overall approach of the 604, differences that will be examined in greater detail ...