The guys at Xtremesystems forum have managed to overclock the $140 three-core AMD Phenom X3 720 all the way to 4.2GHz. They even got the CPU-Z 3.0 validator to second the score.
The guys used Gigabytes GA-MA790GP-DS4H, an AMD 790GX based motherboard, and set the multiplier to 21 and bus speed to 200MHz. Going over 4.2GHz is really an awesome score, especially if you take into account the relatively low price of the platform. The rest of this OC beast included 2x2g OCZ Gold modules doing 5-5-5-15 2.1v @ 1066, PC P&C 750, 2 X hd4850 512mb, OCZ Vindicator, 36gig Raptor,Benq DL DVD burner.
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pretty sweet, just by raising the multi up to 21 they wer able to obtain this clock.