Since nobody else tackled this one, briefly:
Pentium M is a further development of the Pentium 3 architecture.
Pentium 4 is a entirely separate branch of development centered around the "NetBurst" architecture (if I recall the name correctly).
Pentium M has more IPC (instructions per clock) than the Pentium 4, but it runs at a lower clock speed. It also has a shorter pipeline and thus there is less of a penalty for branch misprediction and cache misses.
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