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Does Latency increase with Mem capacity?

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August 2, 2010 11:02:15 PM

Hey folks,

I've been looking at 8Gig DDR3 kits (2x4G), and can't find anything better than CAS Latency of 9. Does the latency increase with memory capacity, meaning I have to choose between speed and capacity?

Too many times in the past I've bought RAM in the "standard" capacity for the time, only to get stuck a few years down the road having to toss it all and buy new, larger capacity sticks in order to increase total capacity. This time I want to avoid that by getting my 8 Gig in 2 sticks, leaving 2 slots to expand to 16Gig a few years down the road. But if I have to sacrifice speed to do it, maybe it's not such a good idea...

Thanks a lot.

-Bill H
a b } Memory
August 3, 2010 1:24:55 AM

You are correct, as you increase capacity, the Latency increase as well. For example, the lowest Latency I've see on DDR3 is Cas6 but DDR2 goes down do Cas3 (DDR2 400). This seems to be the nature of the best. You are better to run with lower latency than you are with higher MHz.

However on the flip side, higher capacity memory gives you the ability to "underclock" and run at tigher timings than you might be able find for DDR3 of equal speeds. Example, G.Skill PI 6GB (3x2GB) DDR3 1600 set runs at Cas7, however the G.Skill Tridents 6GB (3x2GB) DDR3 2000 set runs at Cas( but can be "underclocked" to DDR3 1600 Cas6, which is out performs the PI model.
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August 3, 2010 1:51:51 AM

Ok, makes sense, and that may be what I've been seeing (since I've been almost exclusively looking at DDR3 1333, and wondering why the CL's are so much lower for DDR2 - which also happens to be smaller size). But I'm also wondering whether RAM with a larger storage size (i.e. 4 Gig sticks instead of 2 Gig sticks) would also negatively impact CL?

So, go get 2x4Gig sticks would I have to sacrifice CAS latency compared to 2x2Gig sticks of RAM that is otherwise the same?

Thanks very much.

-Bill
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a b } Memory
August 3, 2010 2:06:47 AM

You are correct again... Larger single stick size (2GB versus 4GB sticks) will have in impact on Latency, as well.

Also, I would typically recommend sticking with a 2x2GB set versus a 2x4GB set, as you'll run into more motherboard stability issues with a 4GB stick in a single DIMM slot. Also, 4GB (2x2GB) is currently enough horsepower for about 96% of all computes in use. You'll have plenty of power at 8GB of RAM (4x2GB), if you decide to go that route.
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August 11, 2010 3:50:47 AM

Best answer selected by harriw.
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