Picking the right memory for SB setup.

bigdogchris

bigdogchris

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I'm upgrading to the Sandy Bridge platform.

What I'm asking is, how do I figure out what speed of memory to purchase so that the QPI link is not bottlenecked? If a CPU is 6.4GT/s QPI, how do I find what memory speed is required? DDR3 speed is anywhere from 1066 to 2500. This is such a basic concept that I can't believe that I can't find information online explaining this. I know there has got to be a way to figure it because I just can't imagine buying a Core i7 SB CPU then sticking in 1066 DDR3 and have everything operate at it's highest performance.

Also, how does the bclk effect QPI? I understand SB bclk is essentially locked, but I want to know anyways.

This is a situation where I want you to teach me to fish, rather than simply giving me a fish. So please don't tell me to just buy the fastest I can afford because then I haven't learned anything.

Thanks.
 
If I understand correctly, Sandy Bridge with their hard lock will pretty much all be K series overclocking, I5 2500K or the I7 2600K. I think the official DDR3 speed is still 1333 pc10600 ram. There will be a RAM ratio so you can run 1600, 2133, or even higher.

Though if the 2600K ES is able to run at 49 multiplier, up from 34, that is almost 45% increase, so from 1333 base to 1933 ddr3 for bandwidth to the CPU, look for a 2000 kit

I'd say even with a conservative 4 GHz you'd probably want 1600 ddr3

Take the MHz you plan to run the cpu at then divide by 2.55 to match the stock 3400MHz to 1333 non overclocked ratio.

The memory controller is in the CPU not the QPI, the QPI handles everything but the RAM and the PCI express for the primary video slots (1)x16 or (2)x8, all other x1 slots, Gb lan, SATA etc go through the QPI to reach the cpu.
 
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Thanks for that info. I'm just wondering though if there is a formula. It was so easy to figure with FSB. Just double it, buy that speed ram and you can run 1:1. I suppose you didn't have to run it 1:1 though and could use a divider. I'm just wondering what the performance loss is going to be though on the Core ix chips.
 
The ram controller runs independent of the CPU frequency so there is no 1:1 anymore. Nor do I thing that matters. lga1366 cpus officially support up to 1066 MHz RAM while lga1156 support 1333 MHz.
 
latency seems to look good on benchmarks but not really make that much difference overall in the real world.
 
m_isom said:
If I understand correctly, Sandy Bridge with their hard lock will pretty much all be K series overclocking, I5 2500K or the I7 2600K. I think the official DDR3 speed is still 1333 pc10600 ram. There will be a RAM ratio so you can run 1600, 2133, or even higher.
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Could you explain this ram ratio? Wikipedia says this about Sandy Bridge:

Improved memory controller with maximum 25.6 GByte/s bandwidth supports DDR3-1600 dual channel RAM and two load/store operations per cycle.
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I bought 2 x 4GB DDR3-1600 dual-channel memory on sale in preparation of my January SB build. I've read DDR-1600 is the highest supported for LGA 1155. You're saying unlocked 1155, such as the i7-2600K, can support faster memory than DDR3-1600? Wont all 1155 motherboard memory standards be dual-channel DDR3-1600? Are you talking overclocking or stock ram speeds?
 
bigdogchris said:
I'm upgrading to the Sandy Bridge platform.

What I'm asking is, how do I figure out what speed of memory to purchase so that the QPI link is not bottlenecked? If a CPU is 6.4GT/s QPI, how do I find what memory speed is required? DDR3 speed is anywhere from 1066 to 2500. This is such a basic concept that I can't believe that I can't find information online explaining this. I know there has got to be a way to figure it because I just can't imagine buying a Core i7 SB CPU then sticking in 1066 DDR3 and have everything operate at it's highest performance.

Also, how does the bclk effect QPI? I understand SB bclk is essentially locked, but I want to know anyways.

This is a situation where I want you to teach me to fish, rather than simply giving me a fish. So please don't tell me to just buy the fastest I can afford because then I haven't learned anything.

Thanks.
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There is no info because RAM doesn't go over the QPI bus, s1155 doesn't incorporate QPI in any way, shape, or form. And the memory controller is attached directly to the CPU. With P67 and a K series you can use whatever RAM multi you want (if its stable for you), so go wild.
Westmere chips used QPI to talk to the GPU die, but sandy is all on one piece of silicon.
 
GLSauron said:
There is no info because RAM doesn't go over the QPI bus, s1155 doesn't incorporate QPI in any way, shape, or form. And the memory controller is attached directly to the CPU. With P67 and a K series you can use whatever RAM multi you want (if its stable for you), so go wild.
Westmere chips used QPI to talk to the GPU die, but sandy is all on one piece of silicon.
Click to expand...

If I'm understanding correctly, I could have bought DDR3 2133/2200/2500 for my SB build because it will work just fine in a 1155 mobo w/K-series CPU? (e.g. ASUS P8P67 Deluxe).

Or are you saying nobody knows what memory standard is supported until CES and the motherboards are released? I bought G.Skill RipJaws 2 x 4GB DDR 1600, but now I'm not sure if it will be the best for 1155.
 
DDR3-1600 should be fine. It'll all be running on ratios anyway, since you can't adjust the bclk with SB, so even 1333 should work - in fact some of the released overclocking results showed 5Ghz SB chips running with DDR3-1333. The maximum speed supported will probably be up to the motherboard manufacturers' implementations - Gigabyte boards were advertising 2133 support.

We don't yet know how the memory controller embedded in Intel's Sandy Bridge CPUs performs, but it's definitely a dual-channel design. Each of the UD7's DDR3 DIMM slots can accept up to 4GB of memory, and the manual says memory speeds are supported up to 2133MHz.
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For a higher end board where the multipliers are allowed, sure, the super high speed ram should work. I really don't know what the top supported multi will be. Whether it would *help* is up for debate. I'm sticking with 1600/7/1.35v, myself.
 
Forceman said:
DDR3-1600 should be fine. It'll all be running on ratios anyway, since you can't adjust the bclk with SB, so even 1333 should work - in fact some of the released overclocking results showed 5Ghz SB chips running with DDR3-1333. The maximum speed supported will probably be up to the motherboard manufacturers' implementations - Gigabyte boards were advertising 2133 support.
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I'll add that VR-Zone reports Asus ROG Maximus IV Extreme maximum memory frequency as 2400MHz.

Stuff the board with up to four sticks of 8GB memory for a total of 32GB. Maximum memory frequency (or divider, rather) is 2400MHz.
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Also, I'm digging that graphical EFI BIOS. I didn't even know that was coming for SB.
 
Yes I was referring to the overclocked speeds of ram. I am pretty sure specification speeds are going to be ddr3 1333 pc10600. I saw one sheet that showed some that had official support for 1600 though I believe that is intended for server chips.

Back on my P4 2.4C I could run ram at a 5:4 ratio 275 MHz FSB to 220 MHz RAM. Then later on I think intel stopped letting you lower ram ratios. I ran Core 2 at 5:6 ratio 333 MHz FSB to 400 MHz RAM

I recall an article about RAM bandwidth vs tight timings where the results were basically even, http://www.pcstats.com/articleview.cfm?articleID=873 referring to the 333MHz 2-2-2-5 to the 500MHz 3-4-4-8 but the 400MHz 2-2-2-5 did pull ahead in the synthetics but the frames per second did not increase near the same pace.

DDR1 400 tight timings were 2-2-2-5, DDR2 800 tight timings were 4-4-4-12, DDR3 I have not toyed with yet.

I am speculating on Sandy Bridge, and I made a mistake on the 26 multiplier... its 34 on the I7 2600K so with 3400mhz to dual channel 1333, 4900MHz should be dual channel 1922 or a ddr3 2000 kit to maintain the ratio to the cpu speed.

http://www.anandtech.com/show/3871/the-sandy-bridge-preview-three-wins-in-a-row/5
"Finally, if you focus on multiplier-only overclocking you lose the ability to increase memory bandwidth as you increase CPU clock speed. The faster your CPU, the more data it needs and thus the faster your memory subsystem needs to be in order to scale well. As a result, on P67 motherboards you’ll be able to adjust your memory ratios to support up to DDR3-2133"
 
With the RAM and CPU getting such high clocks, will there be a bottleneck due to the Bclk being locked?
 
So if I'm looking at getting a 2500K and doing at most a 4GHz OC, what RAM speed should I get? (Yeah, just gimme the fish!)
 
WarriorX said:
With the RAM and CPU getting such high clocks, will there be a bottleneck due to the Bclk being locked?
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bClock is a reference clock, everything that actually carries data runs on a multiplier to it.
 
evilsofa said:
So if I'm looking at getting a 2500K and doing at most a 4GHz OC, what RAM speed should I get? (Yeah, just gimme the fish!)
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I think a 1600 kit would suffice for that level, come January we'll have all the answers and hopefully a nice article on overclocking/memory bandwidth results.
 
GLSauron said:
With P67 and a K series you can use whatever RAM multi you want (if its stable for you), so go wild.
Click to expand...

Forceman said:
DDR3-1600 should be fine. It'll all be running on ratios anyway, since you can't adjust the bclk with SB, so even 1333 should work - in fact some of the released overclocking results showed 5Ghz SB chips running with DDR3-1333. The maximum speed supported will probably be up to the motherboard manufacturers' implementations - Gigabyte boards were advertising 2133 support.
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So memory speed should no longer play a role in you ability to OC, but only in memory bandwidth. More memory bandwidth may or may not net real world results?
 
Don't forget timings. Example: 2000mhz cas6 will have a noticeable HPC improvement over 2000mhz cas9, and in some CPU limited games as well. Tight timings reduce the amount of time your CPU has to wait for instructions, and the fastest CPU is a poor paperweight without them.
 
Memory latency, timings and speed hardly matters anymore with the memory controller on the cpu die. Any decent manufacturer with 6G of 1600 is enough for a little while on x64.
 
There shouldn't be a problem with 1.65v memory, its works with gulftown and westmere, doesn't it.
That said, the RAM I've got for sandy is DDR3-1660/7/1.35v G.Skill ECO.
 
get the cheapest memory and overclock it yourself. Most of the G-Skill, Corsair, Giel ram you see out there has the same IC's. The budget Crucial's overclock better than you would think. D9's were always top of the line DDR2 IC's but have been overshadowed by Elpida.
 
bigdogchris said:
This guide truly answered all of my questions in regards to performance and i7 latency, speed and, channels.

http://www.techspot.com/article/131-intel-corei7-memory-performance/
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Those results are pretty disappointing considering i just bout a set of G.Skill 2133mhz Cas 8 RAM for my i2500k build in a couple of weeks. Hopefully the improved IPC and higher clock speeds from overclocking will mean that SB will utilize higher speed memory a little better than current i7's.
 
Someone in another thread here mentioned you don't want memory over 1.5v for SB. What is the reason behind that?
 
No one is sure what voltage the IMC can handle yet - although I asked one of the reviewers over at Bit-Tech and he said that the board they had handled 1.65V memory just fine. YMMV.
 
Atragon said:
For what it's worth, Gigabyte has posted their memory compatibility lists for the UD4, UD5, and UD7 boards on their site.

http://www.gigabyte.com/products/product-page.aspx?pid=3648
http://www.gigabyte.com/products/product-page.aspx?pid=3647
http://www.gigabyte.com/products/product-page.aspx?pid=3646
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Nice find. They only list 1.5V memory, interesting. Can anyone tell what the difference is between the UD4 and the UD5 - to my quick look at the specs they look the same.

Edit: Okay, so the UD5 has a third physical x16 slot (running at x4). Not sure how useful that'll be.
 
Actually, at least part commonly advertised as 1.65V is on the compatibility list, CMX6GX3M3A1600C9.

I haven't looked at any of the others, so I can't say if there are more

For reference, CMX6GX3M3A1600C9 is rated to 1.65V but has SPD defined voltage of 1.5V according to http://www.corsair.com/en/cmx6gx3m3a1600c9.html
 
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