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Dual vs. Single Channel

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December 15, 2007 4:21:37 PM

I have an Core 2 E6400 CPU that has a FSB of 1066 MT/s. To run memory synchronously at rated FSB, I can use either:
- DDR2 1066 (PC2 8500) module in single channel mode
- DDR2 533 (PC2 4200) module in dual channel mode

Is this correct?

According to this site, the advantage of dual channel mode is nominal at best. If that is the case, why would anyone choose dual channel mode if it means using slower memory in the case where you want to run memory synchronously?

More about : dual single channel

December 15, 2007 4:50:54 PM

you can use dual 1066 or dual 800 4200 is slow and dual 800 is priced real good.
December 16, 2007 4:28:25 AM

Any one?
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December 16, 2007 6:21:41 AM

you want the memory to be dual channel and to be at least the speed of the fsb and upward (PC4200/533 and PC5300 are ok and minimum) but for better performance get the dual channel setup with DDR2-800/6400, and the CPU isnt the only thing to use/access the memory btw.
a b } Memory
December 16, 2007 7:20:13 AM

Quote:
To run memory synchronously at rated FSB, I can use either:
- DDR2 1066 (PC2 8500) module in single channel mode
- DDR2 533 (PC2 4200) module in dual channel mode


Says who? What junk motherboard are you using that forces this? Your FSBs true speed is 266MHz, meaning you need at least DDR2-533MHz for a synchronous setup at stock settings. This doesn't matter if its dual channel or not.

Dual channel memory is faster, but not tremendously so. I believe most apps see around 10% better scores, though its been awhile since I've seen anything on the subject. Seeing as dual channel kits are so common, and aren't any more expensive then single channel, I consider this something that is pretty stupid to turn down.
a b } Memory
December 17, 2007 5:09:52 AM

Quote:
The Core 2 has a front side bus (FSB) speed of 266Mhz x 4 (Quadruple) “1066Mhz”, the ram is running at 266Mhz x2 (Dual Channel) x2 (DDR) = “1066Mhz”


I don't think it actually works that way. My understanding is dual channel memory works by not increasing the frequency of the ram, but by doubling the number of bits that can be "grabbed" at once. The memory controller works in 64bit chucks, using dual channel allows 2x64bits, so it works like a single channel 128bit controller. (this is how it was explained to me when the K8 first came out. The net effect of this might even be the same...)

I do know you don't need to try to match the effective FSB speed. You need to match the "true" FSB, or the "base" speed. If the real FSB is 266MHz, your ram needs to run atleast at 266MHz. (DDR means to multiply by 2, so DDR2-533.) Perhaps someone who knows more can help me out.
December 17, 2007 6:12:22 AM

4745454b said:
Quote:
The Core 2 has a front side bus (FSB) speed of 266Mhz x 4 (Quadruple) “1066Mhz”, the ram is running at 266Mhz x2 (Dual Channel) x2 (DDR) = “1066Mhz”


I don't think it actually works that way. My understanding is dual channel memory works by not increasing the frequency of the ram, but by doubling the number of bits that can be "grabbed" at once. The memory controller works in 64bit chucks, using dual channel allows 2x64bits, so it works like a single channel 128bit controller. (this is how it was explained to me when the K8 first came out. The net effect of this might even be the same...)

I do know you don't need to try to match the effective FSB speed. You need to match the "true" FSB, or the "base" speed. If the real FSB is 266MHz, your ram needs to run atleast at 266MHz. (DDR means to multiply by 2, so DDR2-533.) Perhaps someone who knows more can help me out.
You are right on target. I had the whole RAM thing confused a while back, so I did a lot of reading. The 1:1 is on the base frequency of 266 as you stated. I think the whole 1:1 thing is overrated anyway.

@OP get DDR2 800. It's cheap and you can under clock it to what ever base speed you wind up with 266, 333 etc. This assumes that you want the 1:1, personally I would run it at it's rated speed of 800. Any decent mobo can run your RAM in dual channel and, as 4745454b said, all that does is widen the bandwidth from 64bits to 128 bits. See Dual-channel architecture. I was really disappointed when I benched it. The core2s don't really gain much from increasing the RAM above DDR2 800.
a b } Memory
December 17, 2007 6:40:50 AM

I don't know why they wrote the article like that. I've seen people before write the whole 266 x2 x2 again thing, and I've never seen it work out correctly. The base frequency is all that matters.
December 17, 2007 6:49:19 AM

Nice clarification.

-mcg
December 17, 2007 6:59:29 AM

4745454b said:
I don't know why they wrote the article like that. I've seen people before write the whole 266 x2 x2 again thing, and I've never seen it work out correctly. The base frequency is all that matters.
Earlier I said I was disappointed when I benched the dual channel. Let me clarify, I was pissed off. I read so much BS about double the bandwidth less a little overhead, theoretical of course, that I was psyched. What a let down.
a b } Memory
December 17, 2007 8:22:41 AM

I'm sure synthetic benchmarks show a nice improvement with dual channel memory enabled. The problem is not everything depends on memory bandwidth. Just because you double the memory bandwidth doesn't mean you double your benchmarks score. (for the same reason, just because you setup an AID0 array doesn't mean you double your FPS or cut in half your load times.) Just because you increase your memory bandwidth doesn't mean you see a huge increase in performance, unless you look at only memory scores. Again, from what I've seen, most apps see a 10% increase with dual channel enabled. Considering how cheap dual channel kits are, there is very little reason to turn this 10% down.
December 17, 2007 8:36:30 AM

jaydub868 said:
I have an Core 2 E6400 CPU that has a FSB of 1066 MT/s. To run memory synchronously at rated FSB, I can use either:
- DDR2 1066 (PC2 8500) module in single channel mode
- DDR2 533 (PC2 4200) module in dual channel mode

Is this correct?

According to this site, the advantage of dual channel mode is nominal at best. If that is the case, why would anyone choose dual channel mode if it means using slower memory in the case where you want to run memory synchronously?


Incorrect.
The speed of ONE stick is doubled in Dule chanle in evect buy useing that 2nd stick in all recent (4 year old) MB's.
Get your self some G.Skill or Patriot ram sets. G.Skill is selling for 2X2GB sets...4GB for $69 on NewEgg with an email promo code right now.
It will top off or go beyound whatever your CPU/MB will allow.
It also overclocks very well given the price and if you have XP-64 or that crappy Vista OS your system will use all 4GB's of ram as well.
If you want to pay the high price for Corsair/OCZ ram then your just a sucker for adverts.
December 17, 2007 8:49:52 AM

4745454b said:
I'm sure synthetic benchmarks show a nice improvement with dual channel memory enabled. The problem is not everything depends on memory bandwidth. Just because you double the memory bandwidth doesn't mean you double your benchmarks score. (for the same reason, just because you setup an AID0 array doesn't mean you double your FPS or cut in half your load times.) Just because you increase your memory bandwidth doesn't mean you see a huge increase in performance, unless you look at only memory scores. Again, from what I've seen, most apps see a 10% increase with dual channel enabled. Considering how cheap dual channel kits are, there is very little reason to turn this 10% down.
These were synthetic benchmarks, specifically Sisoft Sandra bandwidth benches. I don't remember the specifics, but they were lackluster at best.
December 17, 2007 8:58:51 AM

Zorg said:
These were synthetic benchmarks, specifically Sisoft Sandra bandwidth benches. I don't remember the specifics, but they were lackluster at best.


My "old" skt 939 with G.Skill DDR1-500 overclocked kicks ass on $600+ DDR2-1200 Corsair/OCZ ram in Read/Write/Copy tests and with a snl core Optron 146 with a 50% OC on stock volts and 3C over room temps on air.
But that is not the question he asked about.

The question was about the guys pick of ram for his system and if sngl channel was better than dbl.
Dbl is 2Xs as fast and the ram I told him about is far better than what other products adverts claim...much more so given the prices as it saves 100's of $ for the same speeds.
December 17, 2007 9:09:23 AM

ZOldDude said:
My "old" skt 939 with G.Skill DDR1-500 overclocked kicks ass on $600+ DDR2-1200 Corsair/OCZ ram in Read/Write/Copy tests....but it is a snl core Optron 146 with a 50% OC on stock volts and 3C over room temps.
But that is not the question he asked about.

The question was about the guys pick of ram for his system and if sngl channel was better than dbl.
Dbl is 2Xs as fast and the ram I told him about is far better than what other products adverts claim...much more so given the prices as it save 100's of $$$
I don't know about AMD, but I saw very little improvement on my Q6600 with a GA-P35-DQ6 in dual channel, as I said above.
December 17, 2007 9:32:53 AM

Zorg said:
I don't know about AMD, but I saw very little improvement on my Q6600 with a GA-P35-DQ6 in dual channel, as I said above.

It is all about what you have and WHAT you do with it.
Your MB as good and popular as is is could nerver OC as high as a DFI MB.
PSU's also take their place when OC'ing.
None of the highly adverted PSU can come close to a PC Power & Cooling unit ever. Ram is the same way.
Getting the best out of what you use even if they are NOT the top end item often out preforms the high end adverted product and for FAR less.

I build and OC for others than myself.
Whatever the people want I can and do make run much better.

The ram I told him about WILL out preform Corsair/OCZ for 100's less Dollars when OC'ed vs their high end products stock.
December 17, 2007 11:00:41 AM

I don't care about the Brand of RAM, use what ever you want. I am specifically talking about synthetic bandwidth benchmarks in single channel VS dual channel configurations. Not that it has anything to do with it, but I have a Silencer 610 at about a 50% load.

What I said, and I'll say again, is that the synthetic bandwidth benches for dual channel over single channel did not show anywhere near 100% improvement. I don't have them handy, but the bandwidth increase sucked. I was very disappointed with what I saw, given all the hype.

I'm not saying anything more or less than that. I don't care how well DFI mobos OC or how good G.Skill or Patriot RAM is. It has no bearing on the question or what I was saying, it only clouds the issue.
a b } Memory
December 17, 2007 7:34:05 PM

ZOldDude said:

The question was about the guys pick of ram for his system and if sngl channel was better than dbl.
Dbl is 2Xs as fast and the ram I told him about is far better than what other products adverts claim...much more so given the prices as it saves 100's of $ for the same speeds.


Links please. Disabling dual channel ram won't make your scores drop by half. If you used to open a zip file in 1min, it won't take 2min if you have single channel ram. Synthetic benchmarks will show a large drop off, but thats why I don't use synthetic benchmarks anymore. Dual channel ram doesn't make your computer twice as fast for the same reason AID0 doesn't halve your load times.
December 17, 2007 10:06:20 PM

4745454b said:
Links please. Disabling dual channel ram won't make your scores drop by half. If you used to open a zip file in 1min, it won't take 2min if you have single channel ram. Synthetic benchmarks will show a large drop off, but thats why I don't use synthetic benchmarks anymore. Dual channel ram doesn't make your computer twice as fast for the same reason AID0 doesn't halve your load times.
What synthetic bench are you using? As I said, Sandra doesn't show a major difference.
June 1, 2009 10:29:22 AM

Quote:
I have an Core 2 E6400 CPU that has a FSB of 1066 MT/s. To run memory synchronously at rated FSB, I can use either:
- DDR2 1066 (PC2 8500) module in single channel mode
- DDR2 533 (PC2 4200) module in dual channel mode

Is this correct?



I have come to the same conclusion.
!