SiS735/745 Memory Issues

copy/past iz http://www.vr-zone.com/#1941


Recently we have done up an overclocking review on the Leadtek 7350KDA board and a memory issue was pointed out that when the CPU is running at 133Mhz and Memory is at 166Mhz as it register a lower performance than at 133/133Mhz. This doesn't apply to just Leadtek boards alone and some readers feedback to me that ECS K7S5A too experience this. This is a strange phenomena as memory at 166Mhz should outperforms considerably. Nevertheless we ask Leadtek engineers for an explanation on this issue and some answers can be derived.
Apparently, it is caused by the internal design of SiS chipset. When the memory speed is faster than CPU system (Async mode), it always add some wait state to wait CPU, that means the bottle neck happens to CPU system. This phenomenon appears on SiS solution, but may be not others. It may be caused by its async mode design in the memory & CPU controllers on 735 chipsets. As SiS745 is just screened from 735 to work on DDR333 mode stably, and add some digital circuit of 1394 therefore the same problem would occur. As you know SiS745 supports DDR333 so by right the memory should be running at 166Mhz while CPU is running at 133Mhz. Therefore this will become a major issue if SiS didn't get it fixed for their SiS745 board. I hope to get some answers from SiS directly. Stay tuned.