will I see a difference with dual channel ram??

[majkmil]

i agree that my mb is probably holding me back. but ive run at 12x200 and the chip is new and getting better, still have more voltage to use so 200 or better stable is not out of tje question

 

[Malakai]

For nforce2 AMD MB, when the dual channel memory is running at the SAME speed as the FSB (aka SYNC mode), there is little benefit in terms of improving the system memory BW. Since the FSB BW cannot absorb/supply twice the BW supplied from/to the dual channel memory when the two are running at same frequency.

For AMD MB, the max system memory BW is FSB x 2 x 8 = 16 FSB MB/s, e.g. FSB = 200 MHz, maxBW = 3200 MB/s, actualBW ~ 3050 MB/s due to some overhead.

You may even be better off just using one module since there is a better chance to get a few MHz of the FSB higher and tigher memory timing. The different between single or dual channel at SYNC mode is only 1-2 % of memory BW.

In my opinion, for AMD nforce2 MB, running dual channel with expensive, matching pair at SYNC speed is wasting the most expensive, top HALF of the memory BW, you won't be able to get that part of the bandwith at all.


BUT on the other hand, if FSB is much higher than memory speed, in the case you use old, cheaper memory, there is a benefit of running dual channel ASYNC mode. Intel chipset has been running memory like this.

E.g. FSB = 200 MHz, PC2400 memory running at 75% ASYNC. The resulting system memory BW will be like running PC2700-2800. 3D mark will show such benefit.

How exactly would I set up a motherboard to run like that when its bandwidth options range from 3:5 all the way to 1:2?
(50% to 200%)? I am thinking if I want my mem at 150 and my fsb at 200 I would run 75% async, but everyone is saying in wrong.

I am specifically talking about the 8RDA
See this thread, since everyone is telling me im wrong (Im saying what you are, and plan to juich some dual channel bandwidth out of my old crucial 2100):
http://forum.oc-forums.com/vb/showthread.php?s=&threadid=177176

EDIT: Just saw your 2nd post, kickass, that helped a lot

 

[hitechjb1]

Malakai

The setup to run FSB at 200 MHz, memory at 150 MHz (ASYNC 75%) for NF2 MB is mainly for using OLD/CHEAPER memory for price/performance reason.

Also there is an overhead involved for running dual channel, so you won't get the theoretical BW = 2 * 150 * 8 * 2 = 4800 MB/s. Further, the FSB BW = 2 * 200 * 8 = 3200 MB/s is the limiting factor. As a result, you would get around a bandwidth of about 2800 MB/s (like running at 175 MHz), a gain of (175-150)/150 = 17% (for free) using slow memory using dual channel. It is about 13% from the 200 MHz memory bandwidth at a memory cost of almost half.

Having said that, but for overclockers who always want to get the max performance out of everything. And also there are PC3200/3500 memory around to match the FSB of NF2. In order to get the last % of memory performance, it is better to run in SYNC mode, even in single channel mode. That is why most people would say running ASYNC in NF2 MB is "wrong".


PS: Why for P4 dual channel, it is always better to run in dual channel. The reason is that the P4 FSB is quad pump (4X) data rate. There is no single memory module that can deliver such bandwidth (since memory is DDR 2X), so in order to fill up the P4 FSB bandwidth, two memory modules are used. On the other hand, for AMD FSB (which is dual pump 2X), one memory module can do the job to fill up the FSB bandwdith.

Hope this helps,

 

[Malakai]

Malakai

The setup to run FSB at 200 MHz, memory at 150 MHz (ASYNC 75%) for NF2 MB is mainly for using OLD/CHEAPER memory for price/performance reason.

Also there is an overhead involved for running dual channel, so you won't get the theoretical BW = 2 * 150 * 8 * 2 = 4800 MB/s. Further, the FSB BW = 2 * 200 * 8 = 3200 MB/s is the limiting factor. As a result, you would get around a bandwidth of about 2800 MB/s (like running at 175 MHz), a gain of (175-150)/150 = 17% (for free) using slow memory using dual channel. It is about 13% from the 200 MHz memory bandwidth at a memory cost of almost half.

Having said that, but for overclockers who always want to get the max performance out of everything. And also there are PC3200/3500 memory around to match the FSB of NF2. In order to get the last % of memory performance, it is better to run in SYNC mode, even in single channel mode. That is why most people would say running ASYNC in NF2 MB is "wrong".


PS: Why for P4 dual channel, it is always better to run in dual channel. The reason is that the P4 FSB is quad pump (4X) data rate. There is no single memory module that can deliver such bandwidth (since memory is DDR 2X), so in order to fill up the P4 FSB bandwidth, two memory modules are used. On the other hand, for AMD FSB (which is dual pump 2X), one memory module can do the job to fill up the FSB bandwdith.

Hope this helps,

I know all that, but thanks. Its nice that someone else around here knows how bandwidth and bus speeds work. This place is so different from how it used to be....

Anyway, I was a die hard overclocker, but now I'm a broke one. I already have 512mb of pc2100 crucial that does 155-160fsb max timings. For 50 or 60$ I can get another 512mb stick of the exact same memory and have 1gb of memory running at near 200mhz fsb speeds. 1gb of pc3000 would cost quadruple that easily, which is in now way worth a negligible performance increase of running sync mode.

Thanks again, your post in the other thread was a great help. I was not sure if nforce2 would do what I wanted it to do, now I know it does.
When I finish upgrading, Ill let everyone know how it goes. If I can get a gigabyte of crucial giving me near pc4200 speeds, it should be big news. A gig of crucial costs well less than 200$.