So the first shiny new feature in 790GX doesn’t currently work but thankfully there’s another new feature to maintain our interest: the SB750 Southbridge. Ordinarily we’d say that a new Southbridge is as dull as ditchwater as it typically adds USB and SATA ports to the previous version.
That’s very useful but you could hardly call it exciting, so we’re thankful that SB750 has a couple of tricks up its sleeve. The first is the addition of RAID 5, which puts AMD RAID on an equal footing with Intel and presumably keeps the AMD Marketing people happy - even if we think you’d be mad to consider RAID 5 in a desktop PC. If you’re dead set on using integrated RAID you’ll find AMD’s RAIDXpert utility will help you set up your array.
The second change from SB700 to SB750 is the Advanced Clock Calibration Link for AMD OverDrive - ACC for short. The idea is that the new Southbridge connects to unused pins on the Phenom processor to allow you to change clock timings and thus increase the processor speed. This is where the other side of the 790GX comes into play as you can use it to build a gaming PC that ignores the integrated graphics and instead opts for performance all the way.
We installed AMD OverDrive v2.1.2 that we downloaded from the ATI website, since Foxconn didn't provide it on its driver disk.
AMD claims that ACC will allow you to overclock your Phenom by 200-300MHz more than you could previously achieve. In the past we have had pathetic results overclocking Phenom, so we plugged in a Phenom X4 9750 and got to work. This is a 2.4GHz processor that is multiplier locked and runs at 12x200MHz, so our only option was to raise the 200MHz reference clock and ACC or no ACC we couldn’t budge the speed at all.
We then switched to a Phenom X4 9850 Black Edition, which costs the same £129 as the X4 9750 but runs at 2.5GHz and more importantly it is unlocked. We had no trouble raising the speed to 3.1GHz, which is an epic amount for a Phenom, but we were also able to do it with ACC disabled so we have no idea if the credit should be laid at the door of AMD for its chipset or for the latest version of OverDrive or perhaps it’s all thanks to Foxconn.