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CPU-NB benefits only fast RAM? - Page 2

post #11 of 17
I run a 2.75GHz CPU-NB, a 1.47GHz HTT, and ~DDR-1400 on my 555BE, while my 955BE is at 2.9GHz CPU NB, 1.86GHz HTT, and DDR-1380.

CPU-NB is not just the speed of the memory controller, it's the speed of the entire NB; the IMC, the L3 cache, and the crossbar that connects all the cores. It can significantly increase performance independent of HTT or memory speed.

The HTT bus has more than sufficient bandwidth for a single GPU setup and the SB, even when underclocked. I can barely measure the difference between 1GHz and 2GHz HTT link, so I almost always have mine underclocked; it makes my chipsets run noticeably cooler.

While there may be an ideal ratio for memory to CPU-NB speed, I usually ignore it because the faster CPU-NB itself provides larger benefits, in my experience.

Again, CPU-NB speed is not all about memory bandwidth and though that is important, it's just one thing it influences. Intercore communication and L3 performance are at least as critical.
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post #12 of 17
CPU-NB aka IMC-NB (Intergrated Memory Controller / Northbridge). Data sent to the CPU is first sent to the Crossbar, which then distributes it to the different cores of the CPU. That data has instructions to either be stored in CPU Cache, go to system RAM to be stored for easy access, or be sent back out to wherever it needs to go. When it is sent to RAM, the IMC or Northbridge takes the data so that it can distribute it within RAM. If any data is to be called from RAM, the CPU requests it from the Northbridge. This data travels along the CPU to RAM on the HyperTransport bus (HT Link).

Keep HT Link 2000Mhz +/- 100Mhz always. HT Link (Hypertransport bus/link) will degrade performance and increase instability (due to signal degrading) beyond 2350Mhz - and there's no guarantee that yours will go that far without degrading. Having said that, there is nothing gained by overclocking the HT Link - it's merely a pipeline (albeit a pipeline used to carry data for just about everything on the board).

CPU-NB (IMC/NB) should be overclocked as high as you can get it. For each 10% you increase the CPU/NB speed, memory bandwidth is increased 3-4% and latency is reduced 3-4%. The minimum for RAM is 3x the base speed, so for example 1600Mhz RAM would be base of 800Mhz x 3 = 2400Mhz CPU-NB, but that's just for the RAM, you'll still need to close the gap for the CPU. Anywhere from 2600Mhz to 3000Mhz at 4GHZ for example. I run my CPU-NB at 3250Mhz at 4.5GHZ CPU. You may need to bump CPU-NB voltage up to reach those speeds and anywhere up to 1.5v is ok.
Quote:
Originally Posted by Redwoodz;15367658 
You guys have to remember everything is connected and inter-related. There is no reason to run a 3500 NB speed and leave the HTT link at 2000 MHz, it will cap your system memory bandwidth at 16MB/s. High HTT/NB also enables faster communication with the PCI lanes. You have to run faster RAM speeds to get the benefit off the increased bus speeds.

Nothing gained by overclocking HT Link - see above.
Edited by ALUCARDVPR - 10/20/11 at 11:11am
post #13 of 17
Faster ram needs a faster IMC. That's is why AMD CPUs like tighter timings over higher speeds, slow IMC compared to intel.

You are defiantly being held back by your memory. You should be running at least 1600mhz memory at the stock IMC speed.
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post #14 of 17
Thread Starter 
Thanks for the replies guys!
So, the answer is yes that faster ram will scale better with CPU-NB overclocks, but that's not to say I am not going to see a tangible boost.
Would guys recommend me upgrading RAM? I am thinking about getting a 960T and those low voltage snipers @ 1600.
However, I really only am doing this for games, I want results like the anandtech link, and I noticed they were using RAM @ 2000.
But the thing is, all my current games are GPU limited for me, except TF2 which doesn't have a built in benchmark.

For now I'll go install metro 2033 and turn the graphics way down low for its benchmark...
 
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post #15 of 17
Quote:
Originally Posted by allupinya;15350064 
not 100% but tonight ive been playing around

3500nb.jpg

no gain from 3.0ghz to 3.5ghz nb.

That's pretty insane man.

Is that a custom water loop or what?

I could easily push my 1100T to 4.2ghz if I had better cooling =(
    
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post #16 of 17
Quote:
Originally Posted by allupinya;15350064 
not 100% but tonight ive been playing around

3500nb.jpg

no gain from 3.0ghz to 3.5ghz nb.

Crazy volts there, wow. Probably push past 1.6v @ load. Would like to see it those screens with prime 95 running.

You wouldn't see a gain from 3.0-3.5ghz because your memory is holding you back. You're not even at 1600mhz. A system is only as fast as it's slowest part.
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post #17 of 17
Hey OCN ... I have max set NB 3000 on 4Ghz CPU with divider RAM 1666 and timing 9-9-9-24 [stock 1600]
So max voltage CPU is 1.375 [auto] and CPU-NB 1.4v

Something wrong with CPU-NB voltage, good or warning? biggrin.gif
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