Inside the Machine

The Trade-Off: Decode, Cracking, and Group Formation

As noted earlier, IBM’s PowerPC 970 fetches eight instructions per cycle from the L1 cache into an instruction queue, from which the instructions are pulled for decoding at a rate of eight per cycle. This compares quite favorably to the G4e’s four instructions per cycle fetch and decode rate.

Much like the Pentium 4 and its predecessor, the P6, the PowerPC 970 translates PowerPC instructions into an 86-bit internal instruction format that not only makes the instructions easier for the back end to schedule, but also explicitly encodes register dependency information. IBM calls these internal instructions IOPs, presumably short for internal operations. Like micro-ops on the Pentium 4, it is these ...