EDIT: Sorry, the thread title should have read either "DDR3-1600" or "PC3-12800", not "DDR3-12800"...! Hello! I want to build a new Core i7-920 based pc. So far I have bought the CPU itself, it's a retail, boxed Core i7-920 stepping D0, batch #: 3849A. The question is about the memory. I have already ordered 2 x Patriot 6 GB 1600 MHz kits (8-8-8-24), that is "PVT36G1600LLK" Patriot Extreme Performance Viper Series DDR3 6GB (3 x 2GB) PC3-12800 Low Latency DIMM Kit http://www.patriotmemory.com/products/detailp.jsp?prodline=5&catid=23&prodgroupid=110&id=763&type=1 But I did this, sort of on an impulse, and since I have not yet payed & picked up the package, I have started wondering if this was the correct choice. First, I chose this Viper memory because I read that it worked so well in that thread about the 6.4 GT/s QPI speed unlocking on this page http://forums.bit-tech.net/showthread.php?t=165233 And since I want to use the pc also for creating a bit of video and music, I thought that 12 GB would be nice.. ..but since then, I have read that, even if a 3 x 2 GB setup works fine, it may be a lot harder to get a 6 x 2 GB setup working. So I thought that I should maybe choose Corsair XMS3 HX3X12G1600C9 12GB DDR3 6X2GB DDR3-1600 CL 9-9-9-24 Core i7 Memory Kit http://www.corsair.com/products/go.aspx?pn=HX3X12G1600C9 Since this is a 12 GB kit, it is set to a more relaxed 9-9-9-24 / 1600 MHz in the XMP. But - I could maybe set the Patriot Viper manually to the same relaxed 9-9-9-24 / 1600 MHz, instead of using the 8-8-8-24 / 1600 MHz in the XMP (which is meant for 3 x 2 GB, not 6 x 2GB)..? Or is it better to use the XMP's default setting? Then the next question is.. ..if I have 1600 MHz memory, will that be enough bandwidth to have BOTH the unlocked 6.4 GT/s QPI, AND also the CPU overclocked to.. say, 3.2 GHz - 3.8 GHz...? Or will I have to buy a more expensive 2000 MHz memory? Or is the CPU overclocking unrelated to the memory bandwidth..? Or am I just asking for too much when I want to have 12 GB i an overclocked system..? Maybe 6 GB is enough for me, after all.. ..plus that issue with certain large CPU coolers almost blocking the 6th memory socket, so you can't use high-profile memory like Corsair Dominator w/ fan.. (I have never overclocked any CPU / Memory before, so I have many questions!) Finally, some people have written that the 4.8 GT/s QPI is enough for most people, and if that is true for me, then I could instead utilize the 1600 MHz memory bandwidth for overclocking the CPU. (If those are related, that is..) I was not sure whether I should choose Build Advice, Memory or Overclocking prefix for this thread.. - I hope Overclocking was the correct choice!
Forget about the 6.4GT/s .. thats enough for anything... your CPU and GPU will bottleneck way before that. When Overclocking, set the QPI bandwidth to as slow as it will go... It's the uncore speed that gives you bandwidth. Don't leave QPI Bandwidth on auto... manualy set the slowest speed availalble in the BIOS options.. it will still be plenty. Yes.. with 12GB @ 1600 you will have oodles of bandwidth.. just make sure your uncore speed is at least twice your DDR3 rating... so @ 1600DDR, you need QPI/uncore 3200. Better still, go for DDRx2 +1 BCLK.... 3400 in other words. DDR3-2000 seems like a waste of cash to me. You get far greater bandwidth by oclocking the CPU/uncore. DDR3-2000 will require uncore 4200 to get the most bandwidth from it, and I doubt your board will do that. Running it with uncore less than that and you're not even taking advantage of the faster RAM anyway... and will probably result in an unstable overclock. Stick to 1600... that's plenty. PS As there's no such thing as DDR3-12800.. I understood your typo PPS Don't worry about timings too much either. The difference between 8-8-8-24 1T and 9-9-9-24 2T are minimal Uncore speed baby! That's where it's at! PPPS Welcome to Bit Tech
Later, I will have to read (much) more regarding how to do the overclocking in practice. I have not yet decided what motherboard I should choose. Originally I was thinking about ASUS P6T Deluxe v2. However - I started to read "How to overlock the i7" http://www.chilledpc.co.uk/forum/showthread.php?t=9960 and leaned that: BCLK x CPU Multiplier = CPU Clock Speed 133 MHz x 20 = 2667 MHz, the default 920 CPU frequency BCLK x QPI Multiplier = QPI Clock Speed 133 MHz x 18 = 2400 Mhz (4.8 GT/s), the default 920 QPI frequency 133 MHz x 24 = 3200 Mhz (6.4 GT/s), the "unlocked" 920 QPI frequency BCLK x Uncore Multiplier = Uncore Clock Speed 133 MHz x 24 = 3200 Mhz, the default Uncore frequency BCLK x Memory Multiplier = Memory Clock Speed 133 MHz x 12 = 1600 Mhz, the DDR-1600 memory frequency And when looking at that Award BIOS screenshot from Foxconn Blood RAGE http://www.ollyk.com/ocingthei7/biosscreenshot.jpg I was like, "Aha! Now I finally understand!" So I began thinking I should instead choose Gigabyte EX58-Extreme since that one also have Award BIOS http://gallery.techarena.in/data/513/Gigabyte_EX58-EXTREME-BIOS.jpg And, when I looked at some photos of the "AI Tweaker" of the AMI / ASUS BIOS.., I was like "WTF? the CPU multiplier (CPU Ratio Setting) is there, the BCLK Frequency is there.. - but what about the QPI Multiplier, Uncore Multiplier and Memory Multiplier??" Then I found out that you don't set multipliers or ratios ("divisors") on ASUS's BIOS, instead you try set the frequencies directly: http://www.ocforums.com/showthread.php?t=595403 But since some frequencies will probably not match up, like it will be a 41:23 ratio or something weird, then the BIOS will automtically adjust one or more of the frequency values so they become ratios that work, like 2:8, 2:10 etc. At least, that is what I believe after having read about this..! I guess that this will eventually be just as "easy" to do, after I learned through trial and error and got some experience.. Regarding what you wrote about the "UnCore frequency should be DDRx2 +1 BCLK", - only yesterday I read for the first time about UnCore. I don't know much about it yet! I have 2 questions about this: 1) Ehh.. do you mean that, e.g. on the ASUS P6T Deluxe, even if I set the AI Tweaker's "UCLK Frequency" to 4211 MHz, - like it is shown in the screenshot here http://www.overclock3d.net/gfx/articles/2008/12/02235259646l.jpg - the motherboard will not actually use this, but automatically set itself to some other value? Or that the pc will not start at all if I set it to that 4211 MHz value? 2) I googled for "Uncore 4200" and then I came to this page; "Post your highest your highest Uncore Clock!" http://www.evga.com/forums/tm.asp?m=100690990 If I understand it correctly, it says here that, while the Core i7 C0 stepping CPUs could "easily" get to above DDR clock x 2, the new Core i7 D0 stepping CPUs will not easily get to anything higher than DDR x 2. From this, it seems that there could be ways to get to 4200 MHz Uncore frequency with a DDR3-1600, but while it could be done "easily" with C0 stepped 920's, there are very large problems when using the D0 stepped 920 that I have. So - maybe that could be a reason for me to instead buy DDR3-2000, after all..? Eh.. you mean that the default 4.8 GT/s is "enough for anything", right? OK..!?! Well, I guess that makes sense, in a way.. ..since I will raise the Base Clock from 133 MHz to maybe 200 MHz, the QPI multiplier at the default 18 x (for 4.8 GT/s) will make a jump to.. 3600 MHz or 7.2 GT/s. But if I first set it too 24x, to get 133 MHz x 24 = 3200 MHz or 6.4 GT/s, it will become 200 MHz x 24 = 4800 MHz or 9.6 GT/s after setting Base Clock to 200 MHz.. ..and that is maybe too much, then? Or do you mean that I should set the QPI multiplier down to 12x, since that will give me the default 200 MHz x 12 = 2400 MHz or 4.8 GT/s - even after overclocking the Base Clock to 200 MHz..?
That in all likelyhood, the PC will not boot with a 4200MHz uncore.. it's very high. Can't comment on the D0, but from what I've personally found, once passed DDRx3 +3 it actually starts to reduce bandwidth, and ultimately will become unstable. I've tested everything from 2:1 right up to 2X +4, and 2x +2 seems to hit a sweet spot on my board. Maybe, maybe not.. try it and see. I've never tried to go above 3800 uncore, as I started to LOSE bandwidth at my speeds. I can't see how a 4200 uncore would gain much unless you were running VERY fast memory. Yes, a 4200 uncore, and DDR3-2000 would give serious bandwidth, but it all relies on whether your board/chip can deliver that speed. You won't know until you build it, and if not, then you will have to run your RAM well below it's potential. Plus.... You're only planning a 3.3GHz overclock... You'll have more bandwidth than you need at DDR1600, 3400 uncore. Correct. Correct. The minimum QPI data rate available will increase proportionately with your BLCK/ratio settings. Hence the 6.8GT/s in my BIOS screens...(see this thread) as I'm at DDR1520. Just dont use Auto, because it will probably go for the fastest... which will make your overclock more difficult... and acheive nothing in reality, as almost 7GT/s is a stupidly large amount of bandwidth anyway In short... don't worry about QPI data rate... it does little, if anything to oncrease the speed of your rig. Set to lowest available. Even the stock 4.8GT/s provides more bandwidth (apparently) that any desktop computer can possibly need. You're just pushing your system unnecessarily for nothing. [edit] Sorry.. confused you with someone else whan I said you were only shooting for a 3.3 overclock.
