Memory Timing, Overclocking and Performance
Memory is divided into 4 PC performance categories, PC66, PC100, PC133 and the new PC150. Each category has a specific SDRAM ns speed. PC66 SDRAM is a 10ns SDRAM; this ram is used on older Socket 7 CPU's and Intel Celeron. PC100 is a 8ns SRAM, this ram is used on AMD Athlon, Intel Pentium II and Pentium III. PC133 SDRAM is a 7ns SDRAM; it is used on AMD Athlon systems with the +PCI option, Intel Pentium III Coppermine and VIA Cyrix III systems. PC150 is either a 7ns overclocked SDRAM or a 6ns SDRAM, this memory is used when overclocking the front side bus above 133MHz.
The AMD Athlon memory system of tweaking and adjustments differs a little form the Intel form. Athlon motherboards based on VIA chipsets have added a lot of new memory tweaks and overclocking options. On all of the AMD Athlon based systems the minimum memory speed you will require is PC100 SDRAM in order to run the system at default clock speeds. PC133 SDRAM is a very wise option for AMD based systems as it allows for more overclockability and also allows for the use of the new Asynchronous memory clock. We explained earlier how the memory clock works on the VIA based chips so we won't go into detail again. In order to get a good system going you need to find good ram, and the way you tell good ram is to look at its CAS (Column Access Select) settings. Normally it comes in 2 forms, CAS2 and CAS3. CAS2 is the faster of the 2, why is this so?? The number 2 refers to the amount of CPU cycles it takes for the SDRAM to align with the CPU clock cycle in order to send and receive data. CAS2 only takes 2 cycles where CAS3 takes an extra cycle. This can come down to an extra 10FPS in your favorite game. The best idea when choosing memory is to get a CAS2 PC133 SDRAM module such as Mushkin CAS2 PC133 SDRAM or Kingmax rev 1.2 PC133 SDRAM. The reason for this is that when overclocking beyond 133Mhz (using the +PCI clock option) you can lower the CAS2 on the module to CAS3 in order to get a more stable memory speeds.
Another interesting feature for the AMD Athlon range is the DRAM Interleaving. DRAM interleaving is a process what the memory access is divides by the amount you select, normally there are 3 options, disabled, 2 way and 4 way. 4 Way interleaving is the faster of 2 settings and can increase memory performance up to 20%, this option is dependent on the motherboard you buy, some boards have it and some boards don't. Configuring a AMD Athlon system using the AMD Irongate 750 chipset is a lot like setting up a BX motherboard. All the memory options are the same except the new super bypass option, this is a new option built into the later revision of the Irongate chipset, which allows the SDRAM to bypass certain bridges and access paths allowing for faster ram performance.