DDR/General Memory FAQ (2003)

[Karnevil9]

If you put the one 512mb chip in and two 256mb chips in you I think you would lose the dual channel capablitiy, but you would still have 1024 mbs of ram in your board. If you run the 2 256 chips in dual channel you would have 512mb,s plus about 5% to 20% extra bandwith. So you have to decide if the price of another 512mb chip is worth an extra 5% to 20% bandwith of the 1024 mb's that you already havethan you already have. Personaly, for most applications, I don't think you would even use the capability of the 1024mb's unless you do video editing, or some other application that would require a lot of memory resource.

[Floppyman]

So basically in his case he would need 4 sticks of the same size for dual channel to work, i.e. 4x 256mb or 4x 512mb, correct? Thanks in advance.

[Karnevil9]

He would need at least two identical sticks. One in each of the designated slots. My understanding is that all the sticks have to be indentical for it to work, so either two or three 256mb, or two or three 516mb's chip. They would all have to be the same speed, all PC2700 for example.
Someone correct me if I am mistaken.

[TwoRails]

It's a good question. I've never seen a "limit" on what size mem stick to use for DualDDR. We're use to knowing that RAID and the like has to be matched, but I've never seen that restriction in reference to DualDDR. Asus manuals normally say something like 1) you can use any combo, 2) to utilize DualDDR, you have to use slots 1 & 3, or 2 & 3, or 1 & 2 & 3.
TwoRails

[Karnevil9]

In researching whether they have to be identical, Crucials Memory's website says they have to be indentical, while on another computer forum one thread stated that he was running different memeory and it was supported. That is not necessarily to say that it was running dual channel, but the mobo was working. The post didn't show any benchmarks. I also ran across another review that said that AMD CPU can't utilize dual channel mode even if the board supports it. Sorry I didn't post the links, but I was rushing. If anyone comes across more info please post it.

[TwoRails]

DualDDR really has nothing to do with the CPU. It is simply dual memory controllers getting data to the CPU faster. And, I know my AMD runs faster with DualDDR than without.

Also, in thinking along those lines, the controllers for other items (like hard drives, USB, etc) doesn't limit on matched sets, so why would dual memory controllers? One is fetching from one location / address, while the other is fetching from a different location / address.

TwoRails

[Karnevil9]

This sometimes this gets confusing. I was reffering to an article that said that the dual channel platform on the mobo does not work with an AMD chip, not Dual Data Rate(DDR) which is the memory itself. Just from memory, it said something to the effect that the AMD chip will only the bandwith of the speed it is rated at. If bandwith is increased instead of getting to the CPU it hits a bottleneck and the CPU filters it back to the speed it is rated at. So yes, evrrything will work, but just at the rated speed and not higher. That is probably not a very good rendering, so I will try and find the link and post it here.

[Karnevil9]

This is not the article I was looking for, but it is a good explanation of the what we are talking about.

http://www.computer-memory.info/26.htm

Here is the link. see the fourth paragraph under the question of "what is dual channel memory and what does it do."

http://www.amdmb.com/article-display...D=276&PageID=2

This site appears to be aimed at AMD users.

[TwoRails]

Hi Karnevil9 and Everybody,

Thanks for the links, Karnevil9, but I still disagree. Not only has every review I've ever read on AMD systems shown a preformance boost from DualDDR, but also in my own tests, DualDDR was faster than not having it. The performance gains have ranged from 2% to 15% and slightly higher overall system performance gains.

I also don't buy that Intel has any difference in FSB than AMD does. FSB is just that, FSB. So, if CPU Brand X sez it's a 400 FSB unit, and Brand Y sez it's a 400 FSB unit, then Brand Y will not run at a mystical 800 FSB or the manufacturer would already state that it's a 800 FSB. All FSB's have a max, and max is max. To say that it goes more than Max is like saying, "Wow, man, my guitar volumn goes up to 12 !!"

Have to rest my fingers now

TwoRails

[sk8teguy]

Okay, the verdict is in!! As I said earlier, my computer came with 2 256mb memory boards. 1 was in socket 1 of channel 1 and the other was in socket 3 of channel 2. I then added 2 512mb memory boards. I put 1 512 in socket 2 of channel 1, and 1 512 in socket 4 of channel 2. Although the system showed I had 1.5 gig of memory, I did not notice an increase in performance. I then removed all of the boards and reinstalled the 512mb boards. I put 1 in slot 1 of channel 1 and the other in slot 3 of channel 2. Although I only have 1 gig of memory now, I have a significant increase in performance. I now feel that although the MB supported the 2 512mb and 2 256mb boards together, I did not have dual channel capability with the different sized boards. This was the case even though all 4 of the boards are 333 PC 2700. Thank you all for the input.

[Karnevil9]

I just want everyone to know that I didn't post the link because I agree with it, but simply because it was relevant to the conversation and I never seen that information before. The other link seems to suggest the opposite and what TwoRails, myself, and everyone else believe or seem to notice, that Dual Channel capability gives some performance gain. My AMD AthlonXP 2500+ goes to 11

[MrChad]

I thought the lowest speed ram capable of supporting Dual channel memory was DDR400 (PC3200)?

I'm not too familiar with many AMD MB's but I can't recall seeing any advertised dual channel PC2100/2700 ram.

My particular ram (DDR400) {256mb x2} and MB Soyo dragon 2 support Dual channel, but since my cpu FSB is less then 800Mhz my ram 'under-clocks?' to 266MHz PC2100 speed and can't be changed in the Bios, until I upgrade the CPU later down the road.

Not that dual channel memmory and a 2.4 Celeron chip would do much good for my vast iTunes/MP3 collection.

[Karnevil9]

My Soltek 75-FRN-R mobo says it supports Dual Channel memory from DDR266/DDR333/DDR400. The Kingston PC2700 ram I have are running at 166mhz on the mobo, which would equate to 333mhz, (166X2), and the AMD CPU has 333FSB. The bios lets me choose the settings for the various ram it supports. I don't know why your mobo would be underclocking your ram speed.

[sk8teguy]

I can't think of a reason for your MB to be underclocking your RAM either. I have a Pent 4 300mhz processor and the two of my (166) 333 mhz PC 2700 512 mb of RAM is definetily running as dual channel now. My MB manufactuer and my HP owners manual also show my system supports DDR 226/Pc2100, DDR 333/PC2700 and DDR 400/PC3200 in the dual channel mode.

Sk8teguy

[MrChad]

My MB mfg., Soyo, actually states that my Motherboard which supports 400/533/800MHz FSB CPU's will only run dual channel 200MHz on DDR400 ram when running 800MHz FSB cpu. When using DDR400 ram with a 400 or 533MHz FSB cpu the Bios will lock the speed as single per that CPU's assigned speed. As such my ram is locked at 266MHz single channel. If I get P4 800MHz FSB it will change to dual channel mode and adjust accordingly when and if I have the ram in slots 1 and 3, as I have them now.

I didn't notice this however until I purchased the Motherboard. Kingston ram even informed me that this is as it should run when I called. (BTW Kingston has the coolest and quickest Tech Support I have ever used.)

My chip set is an Intel i865PE MB.
MB: Soyo P4I865PE plus Dragon 2.

[Karnevil9]

If I am understanding your post correctly it seems to me that, if your bios is showing a memory speed of 266mhz and your running DDR ram then the MHZ is the speed times two. If that is the scenario with your mobo, then a listed mhz of 266mhz would equate to 533 mhz when running DDR. As in my mobo, I set my mhz to 166 in order to give me 333mhz when running DDR ram. The 166 would only be applicable if I was using SDRAM. Since you have PC3200 400DDR your mobo should be set to 200mhz for your memory speed. It may still run in single channel because of your mobo's make up but you would still have the full rated speed of your memory, minus the small extra percentage you would get with dual channel mode enabled.

[MrChad]

Well, my motherboard can't run any faster then the slowest link. The cpu is holding everthing back right now. a 400MHz FSB cpu like my Celeron can only fully use Pc2100 ram, so no matter what I install the fastest it will run is PC2100-speed.

A 400Mhz Intel chip from what I have gathered is very slow compared to say 400Mhz AMD chips. I guess this is because unlike the AMD intel is actually a 100Mhz x4 FSB cpu.

[smnsam]

does Intel 865perl has duel channel mem?

[sk8teguy]

I don't know if it does or not? Anyone else know?

[TwoRails]

Per the link below, it supports DualDDR:

http://www.hardocp.com/article.html?art=NDc1

TwoRails

[Karnevil9]

I still don't understand why your Mobo limits you to you to ram that is running at only half the speed of the CPU.

I don't know if this was asked already, but do this board have any jumpers that are set from the mobo, and are they set to the correct speed. It sounds like it is kicking back to a default setting.

[MrChad]

As it was explained to me by Kingston only an 800MHz FSB bus CPU can fully utilies DDR400 ram. My small little 400MHz FSB CPU can't run the ram at full speed because the CPU can't use it all. As such when my CPU is used with this DDR400 even when used in the dual ram spots the CPU ram combo--(my CPU MB RAM combo) runs the ram in single channel by default.

My motherboard also runs slower in on PC2700 ram w/ (800MHz FSB Cpu) situation, in this case however the CPU's FSB speed is limiited instead of the ram, even when used in Dual channel mode.

[Karnevil9]

Then it seems that the Mobo manufacturer is not being on the up and up when it says that it supports an 800 FSB CPU and 400 DDR ram. If it can't handle the bandwith of the memory and CPU then it doesn't support it. If it kicks the memory back to a slower speed, then it does what any mobo will do when memory speed is more than it will support. It kicks it back to a speed that it does support. What's the point of buying PC3200 or PC2700 ram when it can only run at PC2100 speed? You could've saved some money just buying PC2100 ram.

[RayBORG]

Hello to my fellow computer guru's... I'm new here and seem to already enjoy the site. No cursing and slamming is a real plus to me!

I've read threw this thread and I'm beginning to think that an 800Mhz FSB is fictitious. Am I correct?

[Floppyman]

Nope it's actually a 800mhz FSB. Keep this in mind though:

It's really a 200mhz FSB, but it is QDR (Quad Data Rate) so it's actually 4x200mhz = 800mhz.

Let me know if you have more questions and HTH.

[RayBORG]

Thanks Floppyman... That really didn't help, heh. 200mhz x 4??? My point is nothing communicates with the CPU at 800mhz. The bus may, but who cares? Everything attached to the bus doesn't run that fast. Am I viewing this wrong? I must be missing something.

[Floppyman]

The northbridge actually communicates with the CPU at that speed. And the north bridge in turn also communicates with the memory and AGP for example. By 200x4 I mean the bus is quad-pumped. Think of the analogy I posted on the first page with 4 dots on the wheel instead of two. HTH

[stacy532]

I have a celeron 2.6ghz
on the gigabyte 8ipe100 pro bios it says my ddr is at 266mhz
when I over clock my cpu by increasing it from 100mhz ? it does go over 300 mhz though....
if I have pc 2700 in two slots can you put 2100 or ddr 400 in the other slots ? not that im cheap ....lol

[Floppyman]

I don't recommend mix and matching different ram speeds in your system. Even if it does work, all the sticks will run at the speed of the slowest one(s) in the system. HTH

[rustywood]

wow! this fourm is great! what a wealth of information and no attitudes,for someone like me whos new and learning its great! thanks