Pentium 4 "C" edition is the Northwood - the "old" P4. The "E" chips are the Prescott - the "new" P4. A and B are older P4 chips that should be avoided now, unless price and/or motherboard support is a concern. What's best? I would probable get the 3.2C or the 3.4C. The 3.2E and 3.4E are more expensive and not altogether faster, although they are a bit faster in video encoding. The "C" chips are faster in games, which is what I would be more worried about.