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dual channel pc2-8500: wtf?

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April 23, 2007 12:13:25 AM

I am planning on building a system soon and have a couple of questions about dual channel. First of all, I am not going to be overclocking and the FSB of my processor (E6600) will be 1066 MHz, so using DDR2-533 chips should give me the exact same performance as a pair of any faster memory chips because the FSB would limit the speed of the memory to 533 each/1066 together, correct? It seems obvious... but then I see things like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Now I understand that you may want to get memory faster than what your processor supports because it will allow you to overclock, but DDR2-1066? Can somebody please explain why in the world anybody would spend the money on this when there won't be a processor, nor a motherboard, that could support the speed of running that in dual channel any time in the near or distant future? I just want to make sure I really understand what is going on with dual channel.

Finally, I saw this in the FAQ:

"The only potential problem: Because you are using 4 memory modules, which require more power, your system may clock the speed of the modules down to maintain stability."

I do intend to use all four memory slots, how often is this an issue? I downloaded some manuals for various motherboards but never saw any mention of this. Is it a common enough issue that I should buy memory at a speed one step up (667 instead of 533) just in case?

Thanks for any clarifications.
a b } Memory
April 23, 2007 12:27:50 AM

Quote:
I am planning on building a system soon and have a couple of questions about dual channel. First of all, I am not going to be overclocking and the FSB of my processor (E6600) will be 1066 MHz, so using DDR2-533 chips should give me the exact same performance as a pair of any faster memory chips because the FSB would limit the speed of the memory to 533 each/1066 together, correct? It seems obvious... but then I see things like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Now I understand that you may want to get memory faster than what your processor supports because it will allow you to overclock, but DDR2-1066? Can somebody please explain why in the world anybody would spend the money on this when there won't be a processor, nor a motherboard, that could support the speed of running that in dual channel any time in the near or distant future? I just want to make sure I really understand what is going on with dual channel.

Finally, I saw this in the FAQ:

"The only potential problem: Because you are using 4 memory modules, which require more power, your system may clock the speed of the modules down to maintain stability."

I do intend to use all four memory slots, how often is this an issue? I downloaded some manuals for various motherboards but never saw any mention of this. Is it a common enough issue that I should buy memory at a speed one step up (667 instead of 533) just in case?

Thanks for any clarifications.


I think I understand your question. You are asking wtf? Memory speed and FSB are two different propositions. PC5300 has a data transfer rate of 5.3 MB per second. PC8500 has a data transfer rate of 8.5 MB/s. At best PC5300 667 mhz. DIMMS will run well over 700 mhz., but well under the default speed of PC8500 1066 mhz RAM. If you have a question about will 2 x 1GB work in conjunction with 2 x 512 MB in dual channel the answer is yes it will.
April 23, 2007 12:33:51 AM

I understand that the PC5300 is at best designed to run much slower than the PC8500. The wtf part of my question was that, assuming dual channel is used, won't they run at the same speed because the external bus of a E6600 (1066 MHz) will be reached or exceeded (and thus downclocked) in both scenarios?

I do not plan to use chips of different sizes, I will be using two pairs of 2x1GB.
Related resources
April 23, 2007 1:16:15 AM

Here's some actual data: http://www.madshrimps.be/?action=getarticle&number=1&ar...
It suggests that running your RAM 2 "steps" or more faster than what is needed to saturate the FSB will actually provide modest performance gains.
Running it 1 "step" faster, especially at slower latencies, can actually result in reduced performance than running it at the FSB-saturating speed.

As for some MBs reducing their max memory bus speed with 4 DIMMs installed, this is programmed into the BIOS and is unaffected by the specs of the DIMMs. It's just a reflection of a lower-quality MB design.
April 23, 2007 1:27:35 AM

Quote:
Here's some actual data: http://www.madshrimps.be/?action=getarticle&number=1&ar...
It suggests that running your RAM 2 "steps" or more faster than what is needed to saturate the FSB will actually provide modest performance gains.
Running it 1 "step" faster, especially at slower latencies, can actually result in reduced performance than running it at the FSB-saturating speed.

As for some MBs reducing their max memory bus speed with 4 DIMMs installed, this is programmed into the BIOS and is unaffected by the specs of the DIMMs. It's just a reflection of a lower-quality MB design.


Thank you, that link is very helpful, and especially relevant given the numbers are taken on a very similar platform to which I will be using. As far as lowering the memory speed due to having all four slots in use, does anybody know which motherboard brands tend to do this? Or which ones don't? I really want to avoid slowing my memory access down due to having all four slots in use, as the reason I want to have all four slots in use in the first place is to get maximum performance from having a large amount of RAM.
April 23, 2007 1:45:16 AM

Your assuming the memory is only run at a 1:1 ratio with the FSB e.g. 200mhz FSB = 400mhz RAM (DDR)

The thing is RAM can also run at ratio's of say 2:5 so a 200mhz FSB would have RAM running at 500mhz (DDR)

There's a lot more to it than that though and I probably haven't even explained it correctly.
April 23, 2007 1:52:32 AM

Quote:
Your assuming the memory is only run at a 1:1 ratio with the FSB e.g. 200mhz FSB = 400mhz RAM (DDR)

The thing is RAM can also run at ratio's of say 2:5 so a 200mhz FSB would have RAM running at 500mhz (DDR)

There's a lot more to it than that though and I probably haven't even explained it correctly.


I don't think I follow you. The only assumption I'm making is the memory runs at 2:1 ratio with itself in dual channel configuration, irregardless of the FSB, until the speed of the FSB is exceeded, at which point, apparently according to the link Mondoman posted, will still increase but at a much slower rate than 2:1.
April 23, 2007 4:23:53 AM

Quote:
... As far as lowering the memory speed due to having all four slots in use, does anybody know which motherboard brands tend to do this? ...

It's not necessarily any specific brands, but in general you should be better off with higher-end boards using Intel chipsets. Check with the manufacturer and/or download and read the MB manual before you buy. Checking out the manufacturer's qualified memory list is also a good idea -- for example, have they tested 2GB modules?
April 23, 2007 5:10:42 AM

Quote:
I am planning on building a system soon and have a couple of questions about dual channel. First of all, I am not going to be overclocking and the FSB of my processor (E6600) will be 1066 MHz, so using DDR2-533 chips should give me the exact same performance as a pair of any faster memory chips because the FSB would limit the speed of the memory to 533 each/1066 together, correct? It seems obvious... but then I see things like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Now I understand that you may want to get memory faster than what your processor supports because it will allow you to overclock, but DDR2-1066? Can somebody please explain why in the world anybody would spend the money on this when there won't be a processor, nor a motherboard, that could support the speed of running that in dual channel any time in the near or distant future? I just want to make sure I really understand what is going on with dual channel.

Finally, I saw this in the FAQ:

"The only potential problem: Because you are using 4 memory modules, which require more power, your system may clock the speed of the modules down to maintain stability."

I do intend to use all four memory slots, how often is this an issue? I downloaded some manuals for various motherboards but never saw any mention of this. Is it a common enough issue that I should buy memory at a speed one step up (667 instead of 533) just in case?

Thanks for any clarifications.


I think I understand your question. You are asking wtf? Memory speed and FSB are two different propositions. PC5300 has a data transfer rate of 5.3 MB per second. PC8500 has a data transfer rate of 8.5 MB/s. At best PC5300 667 mhz. DIMMS will run well over 700 mhz., but well under the default speed of PC8500 1066 mhz RAM. If you have a question about will 2 x 1GB work in conjunction with 2 x 512 MB in dual channel the answer is yes it will.

Goodness could you imagine RAM that actually was that F'in slow? 8MB/s, that is more than a factor of 10x slower than the new Hitachi 1TB drive on read speed.

DDR2 Speeds are dependent on timing as well as speed.

Quote:
Module name || Bus clock || Chip type || Peak transfer rate
PC2-3200 || 200 MHz || DDR2-400 ||3.200 GB/s
PC2-4200 || 266 MHz || DDR2-533 || 4.264 GB/s
PC2-5300 || 333 MHz || DDR2-667 || 5.336 GB/s
PC2-6400 || 400 MHz || DDR2-800 || 6.400 GB/s
PC2-8500 (planned) || 533 MHz || DDR2-1066 || 8.500 GB/s
a b } Memory
April 23, 2007 5:36:09 AM

Thanks for the correction.
April 23, 2007 5:38:55 AM

You're welcome. :D 

Just a typo, GB vs. MB.
April 23, 2007 5:55:42 AM

Quote:
... As far as lowering the memory speed due to having all four slots in use, does anybody know which motherboard brands tend to do this? ...

It's not necessarily any specific brands, but in general you should be better off with higher-end boards using Intel chipsets. Check with the manufacturer and/or download and read the MB manual before you buy. Checking out the manufacturer's qualified memory list is also a good idea -- for example, have they tested 2GB modules?

I'll go back and fix my previous post, but I meant to say two pairs of 2x1 GB for a total of 4 GB. The board I am considering is:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

The supported memory list makes it look like they have done somewhat extensive testing of 1GB chips, and the manual says nothing about downclocking the chip speeds if all slots are used. This motherboard uses Intel chipsets. Do you think I could safely buy this board without having to worry about any speed reduction from using all slots?

Thanks everyone for your help so far.
a b } Memory
April 23, 2007 5:57:05 AM

Tomorrrow my RMA'd 2 x 512 PC5400 kit will arrive fom OCZ technologies warranty service. Again. The first set OCZ sent me under the lifetime warranty were deader than a door nail. Fresh out of a retail package...nothing. Then I have my 2 x 1GB G. Skill PC6400 waiting at the UPS station to be replaced under warranty tomorrow morning. I burned it up overvolting it. Hahahaha! Man that stuff ran boss at 1000 mhz.! Talk about gigabyte transfer rate/s! I thought it was the video card at first. Just the RAM I fried. I ordered my Q6600 tonight. I don't dare put the screws to that puppy! Well, not until I get back all the other stuff I burned up. LOL!
April 25, 2007 9:53:10 PM

So i have pc8500 stuff because i just happened to have a deal on it at the time, and so i thought it would be useful for a quadcore in the future. Im now thinking that my motherboard wont take going up to the speeds that a quadcore and pc8500 could reach? Its only an abit ab9, so if i did finally get a quad and managed to get the ram up to 1:1 (at whatever speed it might be) would the board take it?

Sorry if this is a bit of a noobish question but its late and i cant be bothered to think too hard about it.
a b } Memory
April 25, 2007 10:19:13 PM

Quote:
So i have pc8500 stuff because i just happened to have a deal on it at the time, and so i thought it would be useful for a quadcore in the future.


I have never owned PC8500 1066 mhz. RAM. I just installed a q6600 an hour ago and started using it now. So, in the upcoming days I will poke around overclocking and making adjustments with this. I'm using PC6400 800 mhz. RAM that I clocked well over 1000 mhz. with the e6600 I just replaced. PC8500 would have a significant potential higher end, system willing, than the PC6400 I am using. I wish I had some PC8500 1066 mhz. RAM to try in here.
April 25, 2007 11:00:29 PM

Ok, a little confusion here

First of all there is an internal clock. That clock speed on your Core 2 Duo's internal clock is 266. (This is before your cpu multiplier is applied which gives you your final speed of 2.4Ghz) . So when you buy DDR2-533 your cpu and your ram will run at 266. But since DDR is DOUBLE Data Rate it runs effectively twice the speed of 266mhz, therefore we get DDR2-533. The FSB is QUAD pumped which results in an effective speed of 1066mhz.

So when your internal clock is at 266 and you have ram rated at DDR2-533 you ram an cpu run at a 1:1 ratio. They are both running at 266. Now without any overclocking you can change this ratio. If you were to buy DDR2-1066 you could run the ratio at 1:2, resulting in a cpu speed of 266 and memory speed of 533.

Now typically unless you have really high performance ram, like the theoretical situation i just mentioned, you would rather leave it at a 1:1 ratio cause you want your memory and cpu to be in sync.

The other time high performance memory like that is good is because when overclocking it allows to raise your internal clock to 533, Not only does this allow you to run your high performance memory but it does not limit you when overclocking at all because reaching an internal clock speed of 533 is almost very unlikely. There for you can drop the mulitplier on your cpu to something lower and raise the speed of your fsb and ram. By doing this it relieves any potential bottleneck by the fsb(Which only now the new quad cores have even come to close to being bottlenecked), and increases the speed of your ram.

The speed of your ram does have a good performance benefit, but for the price you pay for that ram its often not the best price per performance ratio.
April 25, 2007 11:38:18 PM

Quote:
...
Now typically unless you have really high performance ram, like the theoretical situation i just mentioned, you would rather leave it at a 1:1 ratio cause you want your memory and cpu to be in sync. ....

Actually, it's more that you don't want to be just one "step" out-of-sync (for example, running dual-channel DDR2-667 with a 266MHz clock/1066MHz data rate FSB). Running the RAM faster than that will bring some benefits. See this article for some data: http://www.madshrimps.be/?action=getarticle&number=1&ar...
April 25, 2007 11:58:08 PM

Which is exactly what i said, unless you have high performance memory the net gain the performance gain is either in the negative or barely any at all.

If you buy DDR2-800 and don't overclock your cpu and run the ram at 400mhz its a complete waste of money as the performance gain is barely any. and as with you said with DDR2-667 the performance is in the negatives, so once again unless you have high performance ram you want to be running asynchronously.
April 26, 2007 7:10:41 AM

Sorry, I was mainly trying to point out that there's nothing magic about being "in sync".
I wouldn't consider DDR2-800 RAM to be "high performance" these days, as it often doesn't cost any more than DDR2-533 RAM, and it seems to give a 5-10% performance increase in some real-worldish programs, as shown in the article.
April 26, 2007 9:54:59 AM

I'm just glad to hear it wasn't just me who was a bit confused on this stuff :)  I never really was looking to do much overclocking, so I decided to go the easy route and get the 2.6 ghz E6600 and push up the FSB to (quad pumped) 1333 mhz, and a memory to match it of DDR-667 (dual channel of course). The memory will therefore run synchronously, and while better performance from, say, DDR-1066 chips could be achieved, I came to the conclusion that this was the most *economical* overclock I could do. Please feel free to disagree or advise otherwise; and if it doesn't get debated, maybe this suggestion will help others down the line who buy the same processor who are looking for a easy, cheap, and safe (only 0.4 ghz) overclock with memory to match the new performance.
April 26, 2007 2:17:38 PM

Yeah, well when overclocking running synchronously provides a much more stable overclock, which will result in a higher overclock. Also just like you said when not running a 1:1 you must run at least two increments higher, so running a 4:5 ratio = bad, anything better than that should net a increase in performance.

There is a very similar discussion going on in another thread, refer to it for anything else concerning the 1:1 ratio. Click Here!

@daveelton,

Since like mondoman said DDR2-800 chips aren't very expensive and while you only plan on running at DDR2-667 if you buy DDR2-800 you can run them at DDR2-667 with tighter timings and also you will know that you will have some head room whilst you decide to overclock slightly higher. In the end when overclocking a core 2 duo moderately you can't go wrong with DDR2-800.

But again if you are set on just to raise it slightly to 333mhz then DDR2-667 is fine. The over clock your doing will net the performance slightly better than a X6800 while only paying for less than half of its price, so i think you've done a very 'economical' overclock.
April 27, 2007 5:49:37 AM

I think you meant "synchronously", not "asynchronously" (which means the opposite) in the first line of your post. :) 
April 27, 2007 5:01:09 PM

You can't read my mind? :p 
April 27, 2007 5:25:35 PM

Quote:
You can't read my mind? :p 


Your mind doesn't become available for general reading until 1k posts... sorry try again. :wink: :lol: 
April 28, 2007 2:13:31 AM

Hmm 9xx and counting!
!