Demands: SDRAM
Though most PC133 SDRAM modules run stable at this clock speed, they usually cannot be operated at a CAS latency of 2 clock cycles. Many types have to be run at CAS 3, which reduces the system performance by few per cent. At first sight, it does not sound much, but remember that the difference between two processor speed grades (e.g. PIII 650 and 700) is usually about the same!
We have always been using highest quality SDRAM memory from Micron/Crucial, Memory Solutions or Wichmann Workx (Germany), which can be operated at CAS 2. Even when "only" running 150 MHz you may be forced to reduce the CAS latency time from 2 to 3 clock cycles. At 166 MHz, not even one of our different memory modules runs stable at CAS 2.
Well, I think you understand what I am figuring out right now. If an average SDRAM module can only be run at 133 MHz using CAS 3, the timing would have to be increased even more at higher clock speeds, which of course is impossible. Thus forget CL3 SDRAM for this undertaking.
In order to have the system running stable, I had to reduce all SDRAM timings to the slowest options: CAS 2, RAS-to-CAS 3 and Precharge Time 3.
Asus CUSL2
I had two interesting motherboards available for this project: AOpen AX3S Pro and the Asus CUSL2. The Asus finally made it, because the AOpen board operates the main memory at only 140 MHz when running 166 MHz FSB due to some limitation of its clock generator. A comprehensive 815 motherboard round up is scheduled for the next weeks. Than we will also introduce the AX3S Pro in detail.
The CUSL2 is a typical Asus motherboard as it gives you excellent quality teamed with performance and overclocking features. Making use of the ICH2 chip, the two IDE ports are UltraATA-100 compliant. Six PCI slots, AGP 4x and the AMR slot are provided.
The system did not want to run stable at 166 MHz FSB when I installed more than one memory module. Obviously the timing is already at the limit using one module.