a memory divider is a ratio or a percentage that can be used to change the frequency the memory runs at relative to the processors FSB. in other words you can use it so the memory runs at a chosen fraction of the FSB e.g. 9:10, the memory will run at 9 tenths of the FSB so at stock speed of 200mhz that would have your memory running at 180mhz. as you start to overclock the memory will remain at that fraction of the FSB so if you hit say 250mhz your memory would be running at 225mhz (DDR450)