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NB Frequency

post #1 of 10
Thread Starter 
What relationship does NB frequency have to OC? I have seen NB frequencies in the range of 2400 to 2600. I do know that as I raise my FSB frequency the NB frequency goes up along with the ram frequency. I have only put a slight OC on my CPU from 3.0 to 3.1. My ram frequency is already at 1650, so I would have to drop ram to 1333 if I wanted to OC any farther. Does the NB frequency have any relationship to ram frequency? I do know that a higher NB frequency gives better ram operation. Just trying to find out what role the NB frequency plays in OCing.
LL
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post #2 of 10
The short end, not much.

The hyper transport and NB speeds are related to each other. To raise HT, NB has to match.

The job of the north bridge is to provide a connection of the processor to the rest of your I/O of various buses and speeds, from PCI to RAM, and HT is part of that connection. HT is also involved when cores reach into cache, or each other's cache.

Since the job of the HT/NB combination is to provide a coupler to the various buses of different speeds, the whole idea is that the CPU's speed is independent of that, and so it hardly makes much difference.

Obviously if HT and NB are run faster, we'd expect some kind of performance increase, but you have to really look for it to notice it, and it's not going to be obvious in many cases.

If the stock HT/NB speed can saturation your RAM speed already, increases in HT/NB aren't doing to be noticeable.

However, in a narrowly focused set of benchmarks, you can notice a minor increase in speeds associated with cache operation or inter-core performance, but it's quite minor and has little impact overall.

There MIGHT be an occasion where lowering HT/NB could let you raise the clock using FSB, if otherwise the HT/NB would become unstable, and just maybe there's an extract couple of MHZ that might fall into place because of an odd phase relationship between the different operating speeds of HT/NB to CPU, but I doubt you'd be able to pick up on it easily.

Obviously jumping from HT 1 to HT 2 and upwards can have a significant impact on overall I/O bandwidth, but moving from 2Ghz to 2.2 or 2.4Ghz isn't generally recognizable, though it does offer something when operations are I/O bound, and may be more noticeable with very high speed RAM overclocks.
Edited by JVene - 5/9/10 at 3:29pm
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post #3 of 10
Thread Starter 
Thanks for the info.
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post #4 of 10
Quote from AMD:

Quote:
CPU NorthBridge Performance Tuning
The CPU NorthBridge (CPU NB) clock speed determines the efficiency and bandwidth capacity of the Memory
controller. L3 cache runs at this frequency as well. CPU NB performance tuning gives a measurable boost for
overall system performance. In particular it can reduce the Memory latency and improve L3 cache bandwidth
and latency. In some scenarios the CPU NB should be tuned in order to take the full advantage of overclocked
Memory frequency and bandwidth. In general the CPU NB clock should be at least three times the Memory
clock (example in case of DDR3-1600: 3 x 800MHz = 2400MHz NB clock).
PLEASE NOTE THAT THE AMD PRODUCT WARRANTY DOES NOT COVER DAMAGES CAUSED
BY RUNNING COMPONENTS OUTSIDE OF SPECIFICATION INCLUDING DAMAGES CAUSED BY
OVERCLOCKING (EVEN WHEN OVERCLOCKING IS ENABLED WITH THE AMD OVERDRIVE
UTILITY).
In terms of power delivery and voltage regulation the latest AM2+ and AM3 motherboards have a dedicated
power plane for the CPU NB Voltage rail. The voltage level of CPU NB power plane (CPU NB VID) can be set
independently from the CPU Core Voltage rail (CPU VID).
The frequency of CPU NB is determined by the CPU NB Multiplier (CPU NB FID) and by the HT reference clock
(HT ref. clock, 200MHz by default). CPU NB Multiplier can not be changed on the fly (as various memory
parameters and memory training is based on the NB clock value). A reboot is required in order to adjust the
CPU NB Multiplier. Therefore the performance tuning of CPU NB is mostly done thru the BIOS menu. Note that
CPU NB Multipliers are integer values and therefore the adjustment will be in steps of 200MHz or more
(depending on HT ref clock value). The combination of “HT ref clock” and the “CPU NB Multiplier” adjustment in
the BIOS menu will allow finer steps.
HT reference clock adjustments can be done on the fly via the AMD OverDrive™ utility and this allows finer
granularity for CPU NB Performance tuning and may reduce the time required for tuning (as there is no need to
reboot the system between different HT ref. clock values).
And yes, I see the difference, even with ddr2.
Edited by damric - 7/30/11 at 4:07am
 
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post #5 of 10
Not a 100% on this so I'll ask

I got two Voltage settings in BIOS for NB. When Overclockin the NB do I up the CPU NB VID? or both. And what is the max voltage and temps that the NB can handle?

Right now its at 254x9 (2286) I can up it one more multiplier
Edited by Lefty67 - 5/13/10 at 9:13pm
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post #6 of 10
Quote:
Originally Posted by Lefty67 View Post
Not a 100% on this so I'll ask

I got two Voltage settings in BIOS for NB. When Overclockin the NB do I up the CPU NB VID? or both. And what is the max voltage and temps that the NB can handle?

Right now its at 254x9 (2286) I can up it one more multiplier
You can raise CPU NB VID to increase stability if necessary. This will vary, but I raised mine to 1.3 volts. CPU-NB has same specification as CPU-Core, and increasing it will increase core heat. Keep in mind that the C2 revision Phenoms have a slower CPU NB than the revision C3 Phenoms.
Edited by damric - 7/30/11 at 4:07am
 
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post #7 of 10
Well I got mine to 254x10 at 1.3v

Best I can do without upping the fsb
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post #8 of 10
Thread Starter 
My NorthBidge is automatically set to three times the ram frequency by default. I didn't have to mess with it at all. Ram is at 1500 (750 in CPU-Z) and NorthBridge shows 2250.
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post #9 of 10
This is the simplest and most understandable thread on this topic. I have been hunting and asking about cpu/nb ratio's and the relationship bxn the voltages.

Kudos to every person here.

+1 to everyone in this thread! (even if you just asked the questions!!!)
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post #10 of 10
RAM multi may need to be dropped, but with further increases of the bus clock the RAM speed will go up to 1600Mhz again.

CPU-NB should ideally be 3x or more the RAM speed before dual data rate. i.e. 1600Mhz works best with 2400Mhz+ NB (800Mhz x 3). The CPU-NB is basically the integrated memory controller, which controls access to and from the memory by the CPU.
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