Whats diff between single channel and dual channel Nforce2 400?

[El_Brio]

Thanks!

Is dual channel running two identical stick as "one" virtual stick?

[Bigjakkstaffa]

Duel channel gives around 5-10% boost in ram performance, you simply have two sticks of equal size, one in each of the first to DIMM slots, and they dont need to be matched pairs despite what teh salesman might tell you, though as a general guide, it helps if theyre from the same manufacturer and speed rating

--Jakk:t

[El_Brio]

So total ram ammount is the whole ammt right - not Halved?

Ex 1 pc 3200 512 and 1 pc3200 512 = 1 gig dual channel?

[ComPooTer]

u got it sir

[Bigjakkstaffa]

1 pc 3200 512 and 1 pc3200 512 = 1 gig dual channel?

Correctimundo

--Jakk:t

[Bluehail]

Lemme guess here. In dual channel memory you have two mem sticks. On first stick say you have only even memory addresses, and on the second odd mem adresses. Therefore if it needs to fetch addresses say 0 to 1 the two memory sticks would dump the data around the same time, eliminating some extra lag.. . Am I close?

[Orris]

Have read up a little on the duel channel Nforce motherboards. For the most part, the Amd based systems really dont utilize all of what duel channel has to offer, where as a P4 will. Basicaly you are still as slow as your slowest component, and in the AMD case the FSB of the CPU. As an example, on a single channel system:

Lets say you have a 166 fsb(333ddr) cpu and the same speed ram(pc-2700....333ddr). The speed between the CPU and the northbridge is 166mhz(333ddr) reffered to as the FRONT side bus. The speed between the Northbridge and the memory module is also 166mhz(333ddr) reffered to as the memory bus.
Now, in somewhat simple terms, a Duel channel system is as follows with the same cpu and ram speeds:
The FSB of the CPU is still 166mhz(333ddr) and the memory bus is also still 166mhz(333ddr) BUT it now has two seperate pathes(both ddr) from the Northbridge to two seperate memory modules. So you do gain more memory bandwidth over the memory bus(between the nothrbridge and the memory modules) but you are still hampered by the FSB(from the CPU to the northbridge).
But, on a system with a faster FSB(such as a P4 with 533) running duel channel you are going to see even greater gains sence you are not near as bottlenecked by your cpus fsb.
There is another factor though, that may come into play, but i am not totally sure on how, and what motherboards will be affected.
Sence the AGP usues the northbridge, IF(as i dont know) it can talk to the memory modules directly from the northbridge, and not go through the cpu, I would think that it(your graphics card) might access one channel of the duel ram(for like texture caching) and the cpu could still be accessing the other channel of ram for its proccessing. IF that is the case, then in gaming apps you might see a significant gain by running duel channels.

Hope some of this helps, and if anyone can add to it, or correct any errors...please do.

[$1500-P4 gamer]

Really it dont have to do with the fsb really either. Its cause of the stages in pipe of each cpu. The P4 has 2x as many as XP. XP worked better on sdr and low spd ddr for that reason-more efficient use of bandwidth since 10 stage pipe like P3's and such had. The p4 needs to keep data right there in mem waiting for cpu more than XP does as any lag on input tp P4 ='s serious slow down. Any bad data means refetching and waisting all 20stages in one cycle (P4) till new data fetched. Thats very-very bad. THat ='s twice the lag per any bad data chunk vs. XP. Due to P4's inefficiencys of bandwidth and long pipe. SO it NEEDS tons of bandwidth to make up for its weaker areas. Which it tries to counter with high fsb to keep flow balanced. XP is totally dif than that. This is why 200fsb or 166fsb benches almost identical on my system at 3100+ and 3200+ oclock lv's.

P4 went high mhz low IPC. That means per mhz =' weaker. So more mhz needed. Longer pipe (20stage) than XP (10 stage). Which means any refetching of data is bad. Also means needs 2x more bandwidth to keep pipe full. Dont expect XP to gain from bandwidth it dont need-is the real point. 200fsb on XP is just to keep up with the Jones's. I.E. Intel has top speed of 200fsb so does AMD. Nothing more to it then that. Higher fsb on XP is like 2% gain. WoW. LOL. DCDDR 5% if synched fsb-15% if running asynch. Thats asynched where the CPU fsb is higher than the mems. The other way around it dont help really.:t

[RamonGTP]

Originally posted by Orris
Have read up a little on the duel channel Nforce motherboards. For the most part, the Amd based systems really dont utilize all of what duel channel has to offer, where as a P4 will. Basicaly you are still as slow as your slowest component, and in the AMD case the FSB of the CPU. As an example, on a single channel system:



Thats not correct... AMD's architecture is totally different than that of the P4 and doesn't NEED a high fsb to be efficient. For example, you can overclock a Barton 2500+ to 3200+ speeds using only the multiplier. And even though a true 3200+ has a 200MHz fsb, and the 2500+ a 166MHz fsb, the performance between the two won't be that different. Sure a true 3200+ with a 200FSB will perform a little better, but not what you'd expect to gain from a FSB jump like that. AMD really didn't even need to go to 200, they just did to have a product comprable to the P4C.

[Orris]

Ok, so you are saying that the AMD really DOES utilize duel channel ram more then the P4.....
explain that....

[Orris]

Just incase you misunderstood what i was trying to say...
I said nothing about the AMD needing a high FSB to outperform a P4....i said that the AMD will not utilize what a Duel Channel system has to offer...where as a P4 will. I really could care less what the FSB is, wether its 166 or 200 does not matter....if its running syched with the ram...on a duel channel system there is little gain for the AMD. The extra bandwidth that is gained between the NB and the Ram cannot be utilized because the FSB of the cpu. The numbers from many differnet benchmarks, and my own test show this. A single system and a duel system score within 3-6% of each other...that is NOT utilizing the Duel channel system.

[$1500-P4 gamer]

Originally posted by Orris
Ok, so you are saying that the AMD really DOES utilize duel channel ram more then the P4.....
explain that....

Who said that-where? I said XP is more bandwidth EFFICIENT. BIG-no huge dif. That means it needs less-therfore gains less from more. Make sense? Your confusing bandwidth bottlenecks and whatnot with Bandwidth efficiency which was the REAL question here. Synhced not synched-has nothing to do with it. More of somthing just dont always mean more performance, ask Intel-LOL (more mhz-WAY lower IPC) ask AMD (200fsb-5% gain).......;) :t

[Orris]

Actually P4gamer my statement was not directed at you, but at RamonGTP who quoted me and then replied that I was wrong. What he quoted was
Have read up a little on the duel channel Nforce motherboards. For the most part, the Amd based systems really dont utilize all of what duel channel has to offer, where as a P4 will. Basicaly you are still as slow as your slowest component, and in the AMD case the FSB of the CPU. As an example, on a single channel system:
then he stated the following
Thats not correct... AMD's architecture is totally different than that of the P4 and doesn't NEED a high fsb to be efficient.

I took it that he was saying I was wrong about the AMD based systems not utilizing all of what a duel channel system has to offer. I guess i misunderstood.?
I mean no offense to anyone, and after reading my last few posts i sound as if i did.
So, let me ask you....what advatages does running a duel channel system offer someone using an AMD processor?

[Orris]

The following might clear up what i was meaning:
Single Channel vs Dual Channel DDR Memory

In a motherboard, the CPU is connected to the memory modules (one or two or more) via a memory controller (inside the north bridge).

Single channel memory modules and memory bus

CPU <---- fsb ----> Memory Controller <---- memory bus ----> Memory Module (dimm1/dimm2/dimm3)

maxFsbBandwidth = fsb x 2 x 8 MB/s
maxMemoryBandwidth = memoryBus x 2 x 8 MB/s
x 2 because data is pumped at twice the bus frequency (using both rising and falling clock edges) in DDR (double data rate) form,
x 8 because the memory data bus is 64 bit or 8 Byte wide.

E.g. fsb = 200 MHz,
memoryBus = 200 MHz,
maxMemoryBandwith = 200 x 2 x 8 = 3200 MB/s
(This is why fsb 200 MHz, DDR 400, PC3200 refer to same thing)

In a motherboard with dual channel, two memory dimms can be connected to the memory controller(s) in parallell to provide in theory twice the bandwidth to the memory controller(s)

Dual channel with two memory modules, memory buses in parallel

........................... Memory Controller <---- memory bus ----> Memory Module (dimm1/dimm2)
CPU <---- fsb ---->
........................... Memory Controller <---- memory bus ----> Memory Module (dimm3)

singleChannelMemoryBandwidth = memoryBus x 2 x 8 MB/s
maxMemoryBandwidth = 2 x memoryBus x 2 x 8 MB/s
x 2 because data is pumped at twice the bus frequency (using both rising and falling clock edges) in DDR (double data rate) form,
x 8 because the memory data bus is 64 bit or 8 Byte wide.

E.g. fsb = 200 MHz,
memoryBus = 200 MHz,
maxSingleChannelMemoryBandwidth = 200 x 2 x 8 = 3200 MB/s
(This is why fsb 200 MHz, DDR 400, PC3200 refer to same thing)
maxDualChannelMemoryBandwidth = 2 x 3200 MB/s = 6400 MB/s

So indeed, in dual channel, the memory controller(s) sees twice the memory bandwidth if two memory modules are put into the correct dimms (e.g. dimm1+dimm3, or dimm2+dimm3 for A7N8X). So far so good.

For the current AMD nforce2 MB, the fsb data rate for dual channel is still running as the SAME as a single channel memory double data rate (DDR). Even the memory modules are in parallel to give twice the bandwidth to the memory controller(s), but the fsb CANNOT take advantage of getting twice the data rate from memory controller(s)!!!!

Things are actually more complicated than that for nforce2 memory controller, there is some speculative prefetch data cache in the north bridge to make use of the dual channel bandwidth, so that some data are cached in the NB and can get to the CPU faster than getting from the memory. But the net is that until AMD can provide quad rate (or double fsb speed) than now, there is little or no advantage to make use of the dual memory bandwidth for the CPU. There are some MBs implementing integrated video (a diff version of the NB) which has 2x64 bit datapath and can take advantage of the dual channel memory bus bandwidth.

For current nforce2 MB, maxMemoryBandwidth = fsb x 2 x 8 MB/s
At fsb = 200, maxMemoryBandwidth = 200 x 2 x 8 = 3200 MB/s.
If one can overclock hard (for nforce2) to 220 fsb.
At fsb = 220, maxMemoryBandwidth = 220 x 2 x 8 = 3520 MB/s.

For Intel, the fsb is quad data rate (QDR), i.e. the fsb data rate is four time as fast as the memory bus speed.
E.g. fsb = 166, memory bus = 166 (DDR 333)
maxMemoryBandwidth (quad data rate) = 166 x 4 x 8 = 5312 MB/s
In general, the dual channel memory controller efficiency is not 100%, and also due other bus traffic. So one cannot get twice the memory bandwidth, the effective is around 70-80% = 4000 MB/s.

For P4 dual channel, the effective bandwidth running fsb:memory=1:1 (SYNC mode)= 0.75 x 4 x 8 FSB = 24 FSB MB/s.
E.g. FSB = 200 MHz, effective bandwidth = 4800 MB/s.
E.g running fsb:memory=5:4, with FSB=250, memory=200, effective bandwidth ~ 24 x 225 = 5400 MB/s.

For current nforce2 dual channel, little advantage until AMD fsb data rate is twice as fast as the memory double data rate (DDR). Currently, the fsb data rate is only the same as the max data rate provided by one single memory module.

For Intel P4 chip set, since fsb quad data rate (QDR) is four time as fast as memory speed (or twice the DDR of memory), minus some overhead in the memory controller, the effective bandwidth is about 70-80% of dual channel bandwidth. It is clear 2 modules in dual channel should be used whenever possible.

Summary:

Dual channel or single channel mode in nforce2 mb is not that crucial for overall performance when fsb and memory at running a 1:1 speed (or data rate). The difference is few % (for the same FSB, say 2-3%, maybe 5% (some say 5% but I am not sure) for new NB stepping ?). Also single channel may let FSB to go a few MHz (~ 5-10 MHz at 220, 2-5%) higher due to a smaller chance of potential dual dimm mismatch and memory controller stress at high FSB, I think. On the other hand, dual channel memory controller provides some performance advantage due to its intrinsic speculative caching capability. At this point, the little higher FSB from single channel offset the performance advantage of dual channel, and the two is within 1-3 % either way (depends on overclocked FSB speed, motherboard, memory modules, NB stepping, applications), I think, for AMD mb. For some nforce2 mb that have integrated video which can benefit from twice the nforce2 memory bandwidth, since the bus between the video and the memory controller has 2x64 bit bus.

The max bandwdith for DDR between memory controller and CPU would be 2 x 8 x FSB = 16 FSB MB/s. x2 is because of DDR (data are transferred at both rising and falling edge of the FSB clock, x8 because of 8-byte bus or 64-bit bus). The effective bandwidth, taking into memory controller (~95% efficiency), would be around 15.2 FSB. E.g. FSB = 200 MHz, effective bandwidth ~ 3040 MB/s.

Dual channel makes a big difference for P4 dual channel mb though, due to quad pump data of P4 (or QDR). The max bandwidth for P4 dual channel is 4 x 8 x FSB = 32 FSB MB/s. The effective bandwidth, taking into memory controller overhead (~ 75% efficiency), would be around 24 FSB MB/s.

For single channel, max bandwidth = 16 FSB, effective bandwidth ~ 15.2 FSB. Hence the improvement of effective bandwidth of dual channel = (24 - 15.2)/15.2 = 58% for P4 dual channel system over single channel.

E.g. FSB = 200 MHz, effective bandwidth ~ 4800 MB/s, which is around 60% more than that of a nforce2 mb running same FSB 200 MHz.
E.g. running fsb:memory=5:4, with FSB=250, memory=200, effective bandwidth ~ 24 x 225 = 5400 MB/s.

That was taken from OC forums (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983766#post1983766), credit goes to hitechjb1.

[$1500-P4 gamer]

Your still tying bandwidth to fsb-which isn't 100% true. Doesn't matter. If AMD XP had 6x 200fsb it wouldn't use all the mem bandwidth. Its cause of the Pipes. 10 stages per cycle is why. P4 has 20. It needs twice as much bandwidth to be fed. Its designed for it. XP was designed when sdr was in! P4 was made for rdram, it is gonna be mem bandwidth tweaked. Thats what I been getting at.

Also your figures are off on one point. The entire duel concept with Nf2 that is. It isn't two controllers running 100% beside each other like yer bandwidth figures show.... The second one tries to PREDICT what data will be reused and send it in a duel mode. The second mem controller when enabled is hardly every seen. Thats why its not doing much either even if XP could use it all. Now we know the XP couldnt anyhow cause of how it reacts to single ch. ddr400. This is what truly shows the XP's bandwidth cap.

P.S. Your not upsetting me. Im just trying to have a good tech talk. No biggy. I didnt realise who the last post was for so it confused me a tid is all.

[Orris]

Ahh..I think I understand what your getting at. Still a little different from what I have read before, but it makes sence.
Still, wonder why I am not getting any benifit from running in duel channel mode over singel channel. Might be how I have my memory configured....or mabey it just doenst show itself in games as much as other apps. Any suggestions?
here is what I am running
XP Pro
Abit NF7-S Rev. 2.0
Barton 2500+(180 x 12.5) SLK-800U with Generic Fan
2 sticks of 512MB Crucial PC-3200(running at 360)
Radeon 9700 Pro

[Orris]

Ahh..I think I understand what your getting at. Still a little different from what I have read before, but it makes sence.
Still, wonder why I am not getting any benifit from running in duel channel mode over singel channel. Might be how I have my memory configured....or mabey it just doenst show itself in games as much as other apps. Any suggestions?
here is what I am running
XP Pro
Abit NF7-S Rev. 2.0
Barton 2500+(180 x 12.5) SLK-800U with Generic Fan
2 sticks of 512MB Crucial PC-3200(running at 360)
Radeon 9700 Pro