VDD is the northbridge voltage...I had a older few of them that would give out when running past 190+ FSB...it is like the CPU...when OCed it needs more voltage...and the VDD mod was supposed to of done that...well it would of done it if I hadn't of did a bad solder job on it...and 2350 was a max on that board...with a newer NF2 board with the new C1 NB (ultra 400), I bet it could of done around 2.4 - 2.5...