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Advantage of faster memory (DDR3)?

post #1 of 19
Thread Starter 
Ok, forgive the remedial knowledge here, but I am quite clueless when it comes to the advantages of today's high-end DDR3 memory. When looking at stuff like PC12800 and 14400 running at native base FSB speeds of 800 Mhz and 900 Mhz respectively...or even freakishly fast 16000 running at 1000 mhz base; what advantages can we possibly gain from these FSB speeds?

In my limited knowledge, I'm left with the understanding that newer systems gain a small benefit from running a cpu/memory divider past 1:1 and slightly favoring ram. Why? Doesn't this simply cause the CPU to be the bottleneck?

Then, looking at these extreme FSB speeds that no one can even approach with any current CPU, is there any advantage at all to having memory that fast? Sure, I know DDR3 uses less power and provides better bandwidth, but past anything currently reasonable for FSB, like PC11000 running at 687 base FSB..what's the point? Especially considering the latency advantages of DDR2 memory.

Thanks in advance for setting this neophyte straight!
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post #2 of 19
I think the main reason right now for DDR3 is to remove RAM from limiting your overclock. I don't think it will limit overclocking on your Quad because you won't get your FSB high enough. Here's a DDR3 review that might answer some of your questions.
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post #3 of 19
Thread Starter 
Ok, after reviewing it appears the majority of my assumption was true. Anything beyond PC12800 is absolutely not needed at this point in time, since no one can obtain FSB speeds of greater than mid 600's right now with any regularity.

However, one misconception I had that was proven wrong was the latency issue. Yes, while the latency ratings on DDR2 are better than DDR3, they way in which memory operates actually means the total speed of the memory is actually about the same. DDR3 just isn't any "faster" in regards to latency than DDR2. It isn't slower either though.

So what it all comes down to is the benefits DDR3 offers do not really exend to overall speed over DDR2 unless you are at insanely high OC. Even then, there is absolutely ZERO need for PC144000 or higher. However, up to PC12800 can give you some OC benefit, and even on overlapping speeds with DDR2, will give you lower power consumption, lesser temps and possibly better stability at slight OC speeds.

Thanks for pointing me in the right direction! + rep for you!
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post #4 of 19
Quote:
Originally Posted by Hijack! View Post
Ok, after reviewing it appears the majority of my assumption was true. Anything beyond PC12800 is absolutely not needed at this point in time, since no one can obtain FSB speeds of greater than mid 600's right now with any regularity.

However, one misconception I had that was proven wrong was the latency issue. Yes, while the latency ratings on DDR2 are better than DDR3, they way in which memory operates actually means the total speed of the memory is actually about the same. DDR3 just isn't any "faster" in regards to latency than DDR2. It isn't slower either though.

So what it all comes down to is the benefits DDR3 offers do not really exend to overall speed over DDR2 unless you are at insanely high OC. Even then, there is absolutely ZERO need for PC144000 or higher. However, up to PC12800 can give you some OC benefit, and even on overlapping speeds with DDR2, will give you lower power consumption, lesser temps and possibly better stability at slight OC speeds.

Thanks for pointing me in the right direction! + rep for you!
This is not necessary true. First of all, in regards to latency, people don't really understand what it means. See latency is measures in terms of "clocks" and not time. Therefore, you cannot determine the actual time delay of a particular latency with analyzing the speed of the memory as well.

For example, DDR2-800 with a CAS latency of 4, has a timed latency of 10ns.

DDR3-1600 with a CAS latency of 8 also has a timed latency of 10ns.

Now, as to whether or not DDR3 high speed memory is worthwhile. It depends heavily on the application. It probably helps little in a gaming environment, but in many rendering and high data throughput environments like FEA analysis it helps tremendously.
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post #5 of 19
Thread Starter 
That's what I was eluding to. The overall latency of DDR2 and DDR3 is the same, regardless of CAS latency ratings. DDR3 isn't slower, but it isn't faster either.

Operating speed-wise, sure it's faster. However, my main point was, at this point in time, it's almost a waste of money for anything over DDR3 PC12800.
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post #6 of 19
Quote:
Originally Posted by Hijack! View Post
That's what I was eluding to. The overall latency of DDR2 and DDR3 is the same, regardless of CAS latency ratings. DDR3 isn't slower, but it isn't faster either.

Operating speed-wise, sure it's faster. However, my main point was, at this point in time, it's almost a waste of money for anything over DDR3 PC12800.
No. DDR3 has lower latency.

For example,

A high end DDR2 product would be DDR2-1066 CL5. This comes with 8.5GB/s bandwidth and a CAS latency of 9.4ns.

A high end DDR3 product would be DDR3-1600 CL7. This comes with 12.8GB/s bandwidth and a CAS latency of 8.8ns.

So in this example the DDR3 memory gives 51% more memory bandwidth and a 6% reduction in latencies.

The best DDR2 memory available is DDR2-1200 CL5 with 9.6GB/s bandwidth and 8.3ns latency.

This is worse than the best DDR3 memory which is DDR3-1800 CL7 with 14.4GB/s memory bandwidth and 7.8ns latency.
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post #7 of 19
Quote:
Originally Posted by Hijack! View Post
In my limited knowledge, Im left with the understanding that newer systems gain a small benefit from running a cpu/memory divider past 1:1 and slightly favoring ram. Why? Doesn't this simply cause the CPU to be the bottleneck?
You never get 100% efficency out of any memory, and with slack timings DDR2 and 3 almost never even creep above 50% efficency.

To totaly saturate the FSB with memory that is only ~50% efficienct badwidth wise, you'd need to run it at least double the speed of the FSB.

Furthermore, higher memory speed relative to the FSB means that the chipset does not need to sit around waiting for the memory as much and can complete they clock crossing from the DRAM to FSB clock domain that much quicker. In short, higher memory speed = lower tRD at the same timings, and tRD has a massive impact on chipset/memory performance.
post #8 of 19
Quote:
Originally Posted by Blameless View Post
You never get 100% efficency out of any memory, and with slack timings DDR2 and 3 almost never even creep above 50% efficency.

To totaly saturate the FSB with memory that is only ~50% efficienct badwidth wise, you'd need to run it at least double the speed of the FSB.

Furthermore, higher memory speed relative to the FSB means that the chipset does not need to sit around waiting for the memory as much and can complete they clock crossing from the DRAM to FSB clock domain that much quicker. In short, higher memory speed = lower tRD at the same timings, and tRD has a massive impact on chipset/memory performance.
And where did you get your 50% efficiency information?

It all has to do with math. The FSB is 256 bit, the memory is 128 bit. You have to run the memory twice as fast as the FSB in order to make up for the difference in the bit rate.
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post #9 of 19
Quote:
Originally Posted by pauldovi View Post
And where did you get your 50% efficiency information?
Basic arithmetic.

If I'm running dual channel DDR-800, I have 12.8GB/s of potential memory bandwidth (if paired with a 400Mhz quad pumped FSB), yet i'd be lucky to score more than 5 or 6GB/s in an unbuffered memory test.

Quote:
It all has to do with math. The FSB is 256 bit, the memory is 128 bit. You have to run the memory twice as fast as the FSB in order to make up for the difference in the bit rate.
Dual channel PC6400 (DDR-800) memory matches the exact max bandwidth of intels 400MHz FSB (which is 64-bit, not 256, though it does transfer four times per cycle). An FSB of 400x4(quad pumped)) is the same as memory of 400x2(for DDR)x2(dual channel).

With the low efficiencies I've mentioned, you need to have the max theoretical bandwidth of the memory be much higher than that of the FSB to saturate the FSB.
Edited by Blameless - 9/6/08 at 1:49pm
post #10 of 19
Quote:
Originally Posted by Blameless View Post
Basic arithmetic.

If I'm running dual channel DDR-800, I have 12.8GB/s of potential memory bandwidth (if paired with a 400Mhz quad pumped FSB), yet i'd be lucky to score more than 5 or 6GB/s in an unbuffered memory test.



Dual channel PC6400 (DDR-800) memory matches the exact max bandwidth of intels 400MHz FSB (which is 64-bit, not 256, though it does transfer four times per cycle). An FSB of 400x4(quad pumped)) is the same as memory of 400x2(for DDR)x2(dual channel).

With the low efficiencies I've mentioned, you need to have the max theoretical bandwidth of the memory be much higher than that of the FSB to saturate the FSB.
Damn you just blew my mind and made me feel stupid XD Interesting stuff. So my Q6600 with 333x9 ratio and with DDR2 800 is 1:1 meaning its syncd.

Now when I look into cpuz I have a FSB of 1333 ........... no wait im lost.
    
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