Please, please read Tom's guides before posting. This proves to me that you come only to this forum and disregard the hardware reviews they show about the latest.
"sigh", I am patient, so I'll answer you, but you betta start reading or else "SEARCH BEFORE YOU POST". The Palomino is the 0.18m old core, the Thoroughbred is the new 0.13m core, known as Tbred B model, you can find it from XP2400 to XP2600 so far, at 2GHZ and 2.13GHZ respectively. You bought a Palomino, so it runs hotter, draws more power and may not overclock as well. The NEW Tbred B models are not out yet so you won't be able to return and buy the new ones if you wanted to.
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When buying an AthlonXP, please make sure the bus is at 133MHZ, or you will get a lower speed!