Adrian Wong:
"Sometimes called driving strength. This feature allows you to control the memory data bus' signal strength. Increasing the drive strength of the memory bus can increase stability during overclocking. DRAM drive strength refers to the signal strength of the memory data line. A higher number means a stronger signal and is generally recommended for an overclocked module to improve stability. Supposedly TCCD works better with weak drive strength while just about everything else prefers a stronger signal."
BigToe
“If you leave the option at Auto this will set a weak drive strength, this is good for TCCD based modules but bad for anything else. From testing and debugging the board I have concluded the following. Options 1 3 5 7 are all weak, as is Auto, setting. 1 is actually the weakest option with 7 being as close to the normal weak setting DFI will allow us. Options 2 4 6 8 are the Normal settings, with 8 being the highest strength setting. If you are using TCCD you may want to try 3 5 or 7 as the drive settings as they usually seem to allow the modules to clock well. If you are using VX, or the new BH Gold, or any other modules from the OCZ range you may want to try 8 or 6.”
!! Has a Large Influence on Stability !!