the mobiles use LESS voltage, thus they produce less heat. A lot of the of the headroom problems on overclocking is due to the fact, that theres just too much voltage/heat being used on processors, that you cant drive them up any higher. The mobiles are also multiplier unlocked, while all recent (past year) RETAIL Athlon XP's are locked. Thus, unlocked multiplier, lower voltage, thus cooler, allows for a much higher overclock compared to desktop cpu's.
Mobiles are OEM only (7-30day warranties only (depending on your distributer)). 2400, 2500 or 2600 mobiles all do good (note: there are 2 types of mobile 2600's.. one of them is lower voltage then the other mobile 2600's, thus are better overclockers).
Due to being OEM's they also do not come with a Heatsink/fan.
AMD's current flagship is the 939 Athlon 64's.
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