Its my understanding the Tref count works off the MEMCLK signal that is 200Mhz for us running 1:1. And it counts out for 7.8us refresh for 512M sticks. So 1560 @ 200Mhz 1:1 MEMCLK is the correct setting. In other words the FSB clock is not relavent to this discussion, the refresh period is not based off of it. Refresh happens at a fix rate in time, how fast the RAM is actually being accessed isnt involved in the capacitor refreshing function.

The only thing that matters is how big is the stick, and what its rated refresh requirement is. Most 512M sticks are 7.8us, which off the 200Mhz MEMCLK setting is achieved with a 1560 setting for Tref. 7.8us would be something else for one of the dividers....say 180 (9/10), etc. I also believe that refresh occurs on a PER DIMM basis, so it doesnt matter if you have 1 or 2 or 4 DIMMs populated, each has its own refresh access happening in parallel. The only # that matters is the single stick refresh spec of the module.... 7.8us for most 512M sticks.

Funkyness will occur mixing 256M sticks with 3.9us requirement with 512M sticks with 7.8us....since the A64 controller isnt designed to support seperate settings PER DIMM. The only PER DIMM setting I know of is the MEMCLK enable function (accessible in A64 tweaker)....something Oskar should add to the bios for folks using only 2 sticks....shut off the unused DIMMs clocks for higher OC in some instances.