Dividers are what permit you to run RAM at a speed other than that of FSB. Generally, both would be the same. Though, when overclocking CPU and its equivalent FSB is much higher than current memory modules are able of dealing with. So a divider is used, to augment memory transfer speed. What it does, is use multiples of clock. E.g.in a current overclocked P4 setup, CPU's will reach 250MHz FSB. Few memory modules can run this speed.

Though, there are many PC3200 modules, and those would be able to be used with a 5:4 divider. The memory controller knows to run at 4 clock cycles for every 5 of FSB. With the earlier 533MHz FSB CPU's, and a single channel memory controller board, you required to run memory faster than FSB to attempt and make up bandwidth difference. Here 4:5, or 3:4 dividers were helpful, in order to have a higher transfer speed.

There have been many memory incompatibilities with these chipsets, boards that house them, and memory utilized in them. The problem lies in BIOS of boards and SPD of memory. In many cases, most familiar in ABIT IC7/IS7 series of boards, many sticks of memory reject to run any divider besides 1:1, or will run one up to a certain FSB speed. I have similar problem in my Soltek 86SPE-L "Springdale" motherboard. Using OCZ 3700 Gold memory, I cannot enable either 5:4 or 3:2 dividers at any speed. The system simply refuses to boot, despite of what I place timings in bios. Though, I also have two sticks of Infineon PC3200 memory, which are rather happy running any divider at any speed.

To verify to myself that it wasn't a physical problem with the OCZ, I just plugged all four modules into board. Motherboard BIOS' just default timings to slowest SPD detected, which of course was Infineon one. With those timings loaded in, I was again capable of running any divider, which would not have been possible if it was a hardware problem with OCZ. Sadly, there is no way for me to reprogram SPD of OCZ modules found in OEM PC3200, and then gain access to both dividers, and much higher speed the OCZ modules are able of. Just to ensure that I wasn't preventive myself in testing, I also utilized Kingston HyperX 3500 and Corsair XMS 3200 modules. The Corsair would run 5:4, up to about 250MHz on the FSB, but not 3:2. The HyperX showed similar behaviour as OCZ, and would not run either divider. Putting them in with Infineon, dividers were no longer a problem.

I think this problem found in ABIT boards. The solution is to continue for updated BIOS that solves the incompatibility problem. It appears that ASUS and EPoX series of i865/i875 have less problems, and if you are willing to test many modules, would be the better choice for overclocking using 5:4 or 3:2 dividers. 1:1 though, there are no longer any known problems with ABIT mobo's.