Relative to sixth-generation processors, the Pentium 4 incorporates the following architectural improvements which together define the seventh generation and which Intel collectively calls NetBurst Micro-architecture.
Hyper-pipelining doubles the pipeline depth compared to the Pentium III micro-architecture. The branch prediction/recovery pipeline, for example, is implemented in 20 stages in the Pentium 4, as compared to 10 stages in the Pentium III. Deep pipelines are a double-edged sword. Using a very deep pipeline makes it possible to achieve very high clock speeds, but a deep pipeline also means that fewer instructions can be completed per clock cycle. That means the Pentium 4 can run at much higher clock speeds than the Pentium III (or Athlon), but that it needs those higher clock speeds to do the same amount of work.
Early Pentium 4 processors were roundly condemned by many observers because they were outperformed by Pentium III and Athlon processors running at much lower clock speeds, which is solely attributable to the relative inefficiency of the Pentium 4 in terms of Instructions per Cycle (IPC). Ultimately, the low IPC efficiency of the Pentium 4 doesn’t matter because Intel can easily boost the clock speed until the Pentium 4 greatly outperforms the fastest Pentium III or Athlon that can be produced. What superficially appears to be a weakness of the Pentium 4 is in fact its greatest strength.