Recent Build - Change Motherboards?


Feb 4, 2009
Hey All. I recently built my first computer (start to finish, no piecing together over time like I always did). I have the ECS A780GM & Phenom II X3 720. I currently have it OCed to 3.4GHZ on stock fan/heatsink. I want to unlock the mythical 4th core to see what's going on. Is there any way to change my ACC settings on the 780/700 chipset or would I need to upgrade to the 790/750 chipset? I like my current board A LOT, but would be willing to part with it for a new board that is "guaranteed" to open the 720's 4th core. Feedback?
Mobo: Biostar TA790GX (they said you can use any 790GX + SB700 mobo to unlock)
Go to BIOS, modify Advance Clock Calibration to Auto
that's all
now save the BIOS, restart and wait to see the magic...

The success of this mod however, depends on a few factors:

The disabled core AMD notes to be "unstable", should be fit-enough to be at least enabled and working

The motherboard should support the Advanced Clock Calibration feature, which currently only motherboards with AMD's SB750 southbridge chip support

The Phenom II X3 processor should belong to the 0904 manufacturing batch, these should be some of the initial batches of the processor, and may still be found with retailers

The method employed: Set the appropriate BIOS setting for the Advanced Clock Calibration feature to "Auto", save settings and restart. The system will be able to deal with the disabled core, and off load some work to it. Test with Prime95.


Nov 24, 2008
Tomshardware AMD overclocking guide suggests disabling ACC with the PII's because they apparently have ACC built into the chip.


Dec 24, 2008
I think you will have stability issues if you try to OC with the fourth core unlocked. When the CPU's are tested at the manufacturing plant, chips with all 4 cores that are good are sorted into the PII x4 bin, chips that show instability on one of the cores have that core disabled and are then sorted into the x3 bin. If you want a PII x4, buy a 940. I think cutting corners on the CPU is a bad idea.