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RAM Functionality Question - 2 Modules in Quad Channel System?

post #1 of 8
Thread Starter 
I'm looking to upgrade to 2011-3 and have purchased a 5930k and a Rampage V Extreme motherboard - a quad channel RAM setup. I am considering buying a 2x16GB RAM kit to get me started and adding another 2 matching RAM modules later, due to budget constraints.

My question is: What am I losing by using only 2 RAM modules vs using a 4x8GB kit?

I plan on going to 4x16GB when budget allows (near future - maybe a month or two) and leaving 4 RAM slots unpopulated for quite a while. I would prefer 4x16GB rather than 8x8GB to keep doors open for future expansion. A secondary question: Am I losing or gaining anything by chosing 4x16GB over 8x8GB assuming all else equal (speed, latency..)?

This is the 2x16GB RAM I have in mind, although I still have some research to do and haven't fully decided. http://www.newegg.ca/Product/Product.aspx?Item=N82E1682...
post #2 of 8
Using 2 dual channel kits can cause problems, because the programmed primary, secondary and tertiary timings are only valid with 2 DIMMs installed, possibly causing RAM corruption or inability to POST. Many people seem to ignore this since usually getting 2 dual channel kits is cheaper than 1 quad channel kit and think RAM is RAM, then wonder why they get problems later on when installing them.

Of course, it's your money, you're free to do what you want. But be prepared to not be able to run at the advertised speed; You may need to use looser timings, slower frequency, or both.

As far as 8x8GB vs 4x16GB goes, I don't have any knowledge on that. Some skylake tests seem to indicate that while you only have dual channel capability (2 DIMMs working in tandem), populating all 4 slots seems to have a small measurable performance increase, though not a humanly perceptible one.

It remains to be seen if this performance gain occurs on haswell-E. There has not been any testing with this as far as I am aware, so you're free to test for us and show your results.
Edited by ssateneth - 1/29/16 at 2:51pm
post #3 of 8
Thread Starter 
Quote:
Originally Posted by ssateneth View Post

Using 2 dual channel kits can cause problems, because the programmed primary, secondary and tertiary timings are only valid with 2 DIMMs installed, possibly causing RAM corruption or inability to POST. Many people seem to ignore this since usually getting 2 dual channel kits is cheaper than 1 quad channel kit and think RAM is RAM, then wonder why they get problems later on when installing them.

Of course, it's your money, you're free to do what you want. But be prepared to not be able to run at the advertised speed; You may need to use looser timings, slower frequency, or both.

As far as 8x8GB vs 4x16GB goes, I don't have any knowledge on that. Some skylake tests seem to indicate that while you only have dual channel capability (2 DIMMs working in tandem), populating all 4 slots seems to have a small measurable performance increase, though not a humanly perceptible one.

It remains to be seen if this performance gain occurs on haswell-E. There has not been any testing with this as far as I am aware, so you're free to test for us and show your results.

Thanks ssateneth. I always found it puzzling that a quad channel kit is a little over double the price of 2x dual channel kits. I was definitely one of the "RAM is RAM" people.. so long as they're the same brand/speed/timings I didn't think it mattered how they were packaged. I'll have to do some reading up on that.

I think I recall reading that only populating half the RAM slots was better for overclocking. That was quite awhile ago and I'm not sure if it was specific to any one platform. Do you know if there is any truth to that? The idea was 2x4GB could be overclocked higher than equivalent 4x2GB RAM in a dual channel board.
post #4 of 8
There is some merit for OC consequences. Using less DIMMs means less stress on the IMC, and less stress means more headroom. your results may vary.
post #5 of 8
Thread Starter 
Thanks for the help ssateneth. It sounds like I should just be going for a 4x16GB kit straight away. I was trying to avoid the cash outlay all at once, but I guess I'll be better off in the end.
post #6 of 8
Thread Starter 
I've done a ton of reading on the topic now and my conclusion is that most of the theoretical advantages of more expensive memory options don't have any real world benefit.

To answer my own first question; running an X99 board with only 2 DIMMs cuts your memory bandwidth in half (quad channel vs dual channel), but doesn't show much difference when it comes to benchmarks. PCWorld has a nice article about it here

Answer to my own second question appears to be "maybe". 4x16GB might overclock a little better than 8x8GB, but I probably wont notice any real world difference.

Another interesting result of my research is that faster DDR4 didn't show much benefit over slower DDR4. Over 2666, it looks like there wasn't much benefit to spending more money. One explanation was that the increased latency countered the faster speed. This sounds similar to the 1600MHz "sweet spot" I read about years ago when researching for my last DDR3 build.
post #7 of 8
Quote:
Originally Posted by TheNatural View Post

I've done a ton of reading on the topic now and my conclusion is that most of the theoretical advantages of more expensive memory options don't have any real world benefit.

To answer my own first question; running an X99 board with only 2 DIMMs cuts your memory bandwidth in half (quad channel vs dual channel), but doesn't show much difference when it comes to benchmarks. PCWorld has a nice article about it here

Answer to my own second question appears to be "maybe". 4x16GB might overclock a little better than 8x8GB, but I probably wont notice any real world difference.

Another interesting result of my research is that faster DDR4 didn't show much benefit over slower DDR4. Over 2666, it looks like there wasn't much benefit to spending more money. One explanation was that the increased latency countered the faster speed. This sounds similar to the 1600MHz "sweet spot" I read about years ago when researching for my last DDR3 build.

Natural, I had the same question the other day and the consensus was to use a quad setup, especially since the cpu is built for it. Do you have a link to the article about the 2666 vs 3000 and higher ram? I am debating this very purchase at the moment. I have held off buying any ram because I am not sure if I should go 3000 or 2666. One thing for sure, I see that many are using Corsair vengeance 2666 and the 3000 is getting no love. That is telling me something, but I still like to read and understand the differences myself. I'm leaning towards the 2666 though as it seems to be that nice 'tweener ram.

Thanks
Edited by Methodical - 2/3/16 at 7:21am
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post #8 of 8
Thread Starter 
Quote:
Originally Posted by Methodical View Post

Natural, I had the same question the other day and the consensus was to use a quad setup, especially since the cpu is built for it. Do you have a link to the article about the 2666 vs 3000 and higher ram? I am debating this very purchase at the moment. I have held off buying any ram because I am not sure if I should go 3000 or 2666. One thing for sure, I see that many are using Corsair vengeance 2666 and the 3000 is getting no love. That is telling me something, but I still like to read and understand the differences myself. I'm leaning towards the 2666 though as it seems to be that nice 'tweener ram.

Thanks

Unfortunately I didn't bookmark my readings. A quick google search turned up this article from Anandtech, which is one of the ones I read.
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