Mushkin FAQ
Unregistered SDRAM limits the maximum frequency you can run SDRAM reliably with out having to introduce latencies, the reason is that more chips connected to the memory bus the greater the capacitance load.
Higher capacitance loads require more current to drive the signals to the valid voltage levels. So for the best memory bus performance, the less DIMMS the better (we've seen numerous examples of this, where a board will run stable with one DIMM, but lose stability once more DIMMs are added). Of course, less memory may result in better “benchmark performance” for your memory subsystem, but if you don't have enough memory for your applications then there will be an even bigger performance hit on the performance of your whole system than just running your memory at CAS 3.
So if you need more and better memory performance it’s best to select a DIMM with the highest memory density supported by your motherboard's chipset (check your motherboard manual). This results in less chips connected to the memory bus, therefore your memory bus will see less capacitance load.
Some of you may be thinking that Registered memory is a solution to this possible performance inhibitor, but it isn't. While Registered Memory will not significantly load the bus capacitatively because Registered Memory represents a smaller load on the memory bus, Registered Memory incurs an extra clock delay in your memory cycle. This makes CAS 2 registered memory perform like CAS 3 memory!. Registered memory should only be used if you need to install the maximum amount of memory possible. Many motherboard chipsets only allow a total of 384MB (or 128MB modules) of unregistered memory while allowing 1GB (256MB modules of registered memory) although each motherboard chipset varies as to the total and maximum module size it will allow.
There is a new solution to this problem that we are seeing on some newer motherboards. While most motherboard's memory settings revolve around timing issues, a few motherboards are now offering extended BIOS settings which allow users to change the voltage that feeds DIMM slots. This feature is called VIO voltage, and if I were going to get a new motherboard I would make sure that it has the VIO voltage feature. This feature allows you to tweak the voltage fed to the DIMM slots, not just the AGP/PCI bus and chipset voltages. Being able to tweak the voltage for the DIMM slots will allow you optimize the memory bus so you get it to run reliably depending on how loaded with DIMMs the memory bus is.
I have 3 blocks of memory in my set-up, I think they are all different makes, 1 PQI 512MB SDRAM PC133, 1 Apacer 128MB SDRAM PC133 and one more don't know what brand will have take it out to check. Basically I want to know if the problem could be related to bad/cheap memory?
