Originally posted by: lopri
Well, the title of this thread is kinda misleading.. I haven't seen any memory running faster than CPU on current Intel platform.
Obviously you guys are talking about FSB here - and this discussion itself shows a great deal about the imbalance of FSB system and the confusions surrounding it.
Getting back to the OP's question, does everyone here agree then that his system would run better/no different if he ran his ram at 1:1, 333 mhz, with his FSB, instead of running his memory at it's rated 400 mhz?
The following is a quote from Anandtech's latest article, "Overclocking Intel's New 45nm QX9650: The Rules Have Changed". Not sure if this helps or adds to the confusion. Their recommendation, depending on what CPU you have, of starting at an FSB of 400Mhz, may not be doable for some, i.e., I can do 3.6 Ghz (9 x 400Mhz) stable on my Q6600, but prefer to keep it lower due to temps.
"Tuning Memory Subsystem Performance
Earlier, we talked about the importance of first testing your motherboard's memory subsystem before moving to the CPU. When you think about it, the reason is clear. Encountering an error while testing blindly provides absolutely no helpful information as to the source of the problem. Since both the CPU and memory stability are dependent on the FSB it only makes sense that we remove them from the equation and first tune our motherboard at our target FSB. This is accomplished by setting the target FSB (we recommend you start at 400 MHz) in the BIOS, making certain to select a CPU multiplier which places the final processor frequency at or below the default value. Next, loosen up all primary memory timings and set the memory voltage to the modules' maximum rated value. Assuming the system is in good working order, we can now attribute all observed errors to discrepancies in the MCH settings and nothing else.
Preparing to run Prime95's blend test for the first time
Boot the system in Windows and launch an instance of Prime95. From the menu select "Options" then "Torture Test?" and highlight the option to run the blend test (default). Now click "OK" to start the test. The blend test mode runs larger FFT values, meaning the processor must rely heavily on the memory subsystem when saving and retrieving intermediate calculation results. Although a true test of system stability would require many hours of consecutive testing, in the interest of time let the program execute for a minimum of 30 minutes.
If you encounter no errors (and the system is indeed still running), you can consider the memory subsystem "stable" at this point. If this is not the case, exit Windows, enter the BIOS, and try slightly increasing the MCH voltage. Repeat this process until you find you can complete (at least) a 30 minute run with no errors. If for some reason you find that increasing the MCH, voltage continues to have no effect on stability, or you have reached your allowable MCH voltage limit, you may be attempting to run the MCH higher than what is achievable under stable conditions. Setting Command Rate 2N - if available in the BIOS - loosening tRD, or removing two DIMMs (if you are running four) may help. If you find modifications to those items allows for completion of an initial Prime95 test, be sure to continue the testing by reducing the MCH voltage until you find the minimum stable value before moving on.
On the other hand, if you find that you can comfortably complete testing with additional MCH voltage margin to spare then you are in a good position to dial in some extra performance. Whether or not you wish to depends on your overall overclocking goal. Generally, more performance requires more voltage; this means more heat, higher temperatures, and increased operating costs. If efficiency is your focus, you may wish to stop here and move on to the next phase in tuning. Otherwise, if performance is your only concern, decreasing tRD is a great way of improving memory bandwidth, albeit usually at the expense of a higher MCH voltage.
In the end, as long as the system is stable, you are ready to move on to the next step. The insight necessary to determine just what to change and the effect if will have on stability and performance is something that comes only with experience. We cannot teach you this and experimenting further at a later time will help you sharpen these skills.
Select a Memory Divider and Set Some Timings
The latest generation of Intel memory controllers provides a much more expansive choice in memory dividers than ever before. That said, there are only three that we ever use, the most obvious of these being 1:1. Setting 1:1, simply put, means that the memory runs synchronously with the FSB. Keep in mind though that the FSB is quad-pumped (QDR) and memory is double data rate (DDR). For example, setting an FSB of 400MHz results in a 1.6GHz (4 x 400) effective FSB frequency at DDR-800 (2 x 400), assuming your memory is running 1:1. Selecting 5:4 at an FSB of 400MHz sets a memory speed of DDR-1000 (5/4 x 2 x 400). The other two dividers we would consider using besides 1:1 are 5:4, and in the case of DDR3, 2:1.
Regrettably, there are rarely any real performance gains by moving to memory ratios greater than 1:1. While it is true that many synthetic benchmarks will reward you with higher read and copy bandwidth values, the reality of the situation is that few programs are in fact bottlenecked with respect to total memory throughput. If we were to take the time to analyze what happens to true memory latency when moving from DDR2-800 CAS3 to DDR2-1000 CAS4, we would find that overall memory access times might actually increase. That may seem counterintuitive to the casual observer and is a great example of why it's important to understand the effect before committing to the change.
Start your next phase of tuning by once again entering the BIOS and selecting a memory divider. As mentioned earlier, even though there are many choices in dividers you will do best to stick to either 1:1 or 5:4 when using DDR2 and 2:1 when running DDR3. Next set your primary timings - typically, even the worst "performance" memory can handle CAS3 when running at about DDR2-800, CAS4 to about DDR2-1075, and CAS5 for anything higher. These are only approximate ranges though and your results will vary depending on the design of you motherboard's memory system layout, the quality of your memory, and the voltages you apply. You may find it easiest to set all primary memory timings (CL-tRCD-tRP) to the same value when first testing (i.e. 4-4-4, 5-5-5, etc.), and as a general rule of thumb, cycle time (tRAS) should be set no lower than tRCD + tRP + 2 when using DDR2 - for DDR3 try to keep this value between 15 and 18 clocks inclusive."
Facebook
Twitter