Inside the Machine

An Overview of the Pentium 4's Pipeline

Now let’s step back and take a look at the Pentium 4’s basic execution pipeline. Here’s a breakdown of the various pipeline stages.

Stages 1 and 2: Trace Cache Next Instruction Pointer

In these stages, the Pentium 4’s trace cache fetch logic gets a pointer to the next instruction in the trace cache.

Stages 3 and 4: Trace Cache Fetch

These two stages fetch an instruction from the trace cache to be sent to the back end.

Stage 5: Drive

This is the first of two special drive stages in the Pentium 4’s pipeline, each of which is dedicated to driving signals from one part of the processor to the next. The Pentium 4 runs so fast that sometimes a signal can’t make it all the way to where it needs to be in a single clock ...