lol; Cliffs on P4 :
Early P4s, slow and sorta crappy :
Socket 423 Willamette, available from 1.3 to 2.0Ghz, most boards used RDRAM, had 256k L2, and 400Mhz FSB.
Socket 478 Willamette, available from 1.5 to 2.0Ghz, boards started to use Sdram and DDR (845 variants and the VIA clones), same performance as the Socket 423.
Socket 478 Northwood, available from 1.6a to 3.2(3.4?)ghz, in a variety of bus speeds. Type A was 400FSB, B was 533FSB, and the Cs were 800FSB. All the C's had HT for a little performance boost in some apps. The 3.06 was the only 533FSB chip to get the HT. Confusing? Yep. But any Northwood is a decent little performer, easily keeping up with modern Celerons/Semprons due to the far superior cache.
Socket 478 Prescott. Crappy. Avoid at all costs.
Socket 775 Prescott. Still pretty crappy, but yields seemed better, and they didn't seem to be as difficult to cool.
Socket 775 Prescott 2M. Improved, double the cache.
Socket 775 Cedar Mill. Decent.
^^^
Note : this evaluation applies solely outside of competitive standpoints, ie; does not consider the possible scenario that you would be purchasing a P4 vs. an Athlon XP or Athlon 64, etc. It's just meant to help you size up a potential freebie. During the P4's era vs. the AMD opposition, and including some more recent battles :
The P4 Willamette got it's butt handed to it by Athlon 4 / Early Athlon XP.
The P4 Northwood A and B series fought evenly against the Athlon XPs of the day.
The P4 Northwood C series (at 2.8 and higher) notably outran the Athlon XPs (eq; the 3.0C was faster in most things than even the XP 3200+).
The P4 Northwood C series got it's butt handed to it by Athlon 64
The P4 Prescott series got it's butt handed to it by Athlon 64
The P4 Prescott 2M series got it's butt handed to it by Athlon 64
The P4 Cedar Mill series got it's butt handed to it by Athlon 64
The Pentium D series got it's butt handed to it by Athlon X2
The Core 2 Duo series kicked the crap out of the Athlon X2
The Core 2 Duo / Quad series kicked the crap out of the Athlon FX Quad
The Core 2 Duo / Quad series kicked the crap out of the first Phenom X4s