madu Posted February 1, 2006 Posted February 1, 2006 Hey guys... This is not a problem I'm having with my rig. Just a confusion about the HTT and LDT. There was a thread about some problem and there was the issue of the HTT frequency..shold it be LESS than 2000 or should be AS CLOSE AS POSSIBLE to 2000? I thought its as close as to 2000 partly because it says it in the overclocking guide and also being close to 2000 (2120) worked for me than being less than (1590) 2000. Anyway when I told this in the thread somebody said it should be less than and not over the 2000 (this can change depending on the system). Anyway i was doing some reading about the HTT after that to really find out whats happening. This is a good site if anybody wants to read about HTT: http://www.short-media.com/review.php?r=206&p=1 Anyways HyperTransport is a point-to-point communication system. And in the amd64 series(starting from Hammer processors), there is a HT(HyperTransport) link between cpu(memory controller) and the ram, and cpu and the chipset. From what I've read, the bandwidth between cpu and memory is 6.4Gbps and cpu and chipset is 800Mbps (I think).. So here;s my question... When the cpu is at 2000 HTT (default value), i.e. 200(fsb)x5(LDT multi)x2(Dual channel), there bandwidh between mem controller and memory is 6.4Gbps... this is fine with DDR400 PC3200 memory.. these memory work at 200fsb, and at that clock it has a bandwidth of 3200Mbps(PC3200).. with dual data rate this becomes 3200x2=6.4Gbps.. so that is cool.. at stock values, the HTT is at 2000, and this gives a bandwidth of 6.4Gbps between cpu and memory and memory also works at 6.4Gbps.. all is fine.. Now he question is, what if we have DDR500 PC4000 memory? these will run at 250 fsb, and at that fsb they will work at 4000Mbps, giving a bandwidth of 8Gbps. right? but, if we are not supposed to up the HTT and keep it at 2000, no matter how high we go in fsb and memory frequency, is there any advantage? Suppose I got the DDR500 PC4000 memory.. I put the fsb at 250 and run the memory at 1:1.. so my system runs at 250x11=2.75Ghz and memory at 250 clock. and at this clock, my memory will work at 8Gbps. BUT, i will have to bring down my LDT multi from default x5 to x4. At x5 HTT will be 250x5x2=2500..which is too much.. and at x4, 250x4x2=2000.. sweet..! HTT is at 2000.. BUT, at HTT 2000, the HT bandwidth is 6.4Gbps.. but the memory can work at 8Gbps.. So I dont see any advantage of getting DDR500 when my cpu-mem bandwidth is fixed at 6.4Gbps.. Now.. from what I have read, its 6.4Gbps.. I maybe wrong.. If its more than 6.4 then all is fine.. If the HT badnwidth at 2000 HTT is about 12.8Gbps, then it makes sense to keep the htt at 2000.. otherwise, whats the point of getting a high spec rams? Somethings I have mentioned maybe wrong, so excuse for that please. Hope to know you guys opinions on this HTT issue.. Sorry for the long description guys.. Thanks..! Quote Share this post Link to post Share on other sites More sharing options...
Slammin Posted February 1, 2006 Posted February 1, 2006 Yup, it's true, exactly as you understand it. This is why you see very little difference in benches between pc3200 and pc4000 ram on this chipset. This is also why running your memory on a divider doesn't cause a huge performance hit too. This was all a learning experience for me coming from Intel rigs for so long, but with Intel chipsets, you absolutely never want to run a memory divider, and also the faster you run the memory, the better your benchmarks, and it is almost linear too. Quote Share this post Link to post Share on other sites More sharing options...
madu Posted February 1, 2006 Posted February 1, 2006 Hye..cool.. thanks man...! So I guess going for a high clock mem would not have much advantage.. I mean there will be a advantage of the higher frequency, but the memory bandwidth will be the same... hmmm.. Quote Share this post Link to post Share on other sites More sharing options...
Sharp Posted February 1, 2006 Posted February 1, 2006 Hello, Its not fixed at 6400MB/s. Think of it like this, HTT = CPU to Chipset BUS link. FSB = MEM controller to MEMORY BUS link. Both are indepedant from each other. If what you are saying is true, people would not notice any different when overclocking their CPU. See the diagram in this link? http://www.dfi-street.com/forum/showthread.php?t=24719 The reason why using a divider does not = a total loss in performance is because it no longer restricts the CPU to CHIPSET BUS link, as the memory bus is on its own BUS. Quote Share this post Link to post Share on other sites More sharing options...
madu Posted February 1, 2006 Posted February 1, 2006 I think there definitely is a HTT between cpu(mem controller) and memory.. It has been shown in all the tutorials I have read. Infact the HTT bandwidth between cpu and chipset is much slower than the cpu memory HTT bandwidth..It makes sense since now the mem comtroller is not in the chipset.. I think we should make clear the distinction bandwwidth and frequency.. When people overclock their cpu, there will be differences.. depends on what they do.. if the cpu clock is high, calculations will be done faster... What I am saying(well..not my idea, what I've reading..), the BANDWIDTH between the cpu and memory is not gonna change..Therefore, PC3200 and PC4000 will effectivley have the same BANDWIDTH..BUT! PC4000 can operate at 250(stock).. therefore, data will go in and out faster.. but the amount of data going in and out will be same.. but because of the higher data frequency, there is a effective improvement..! and yes.. there will be no much peformance degrade by using a divider because cpu-chipset link is independant.. Well.. I'm just trying to justify what I have understood.. I maybe wrong... Quote Share this post Link to post Share on other sites More sharing options...
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