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Confused about dividers and rated/real FSB/clocks

post #1 of 4
Thread Starter 
Okay, so I'm set up to get myself a Q6600 G0 like so many others, and the last component I need to figure out what to do about is the RAM.
This is my first dedicated overclock ever (I've only dabbled before, and I've never really spent extra on parts to make an overclock work well). I've got an ultra120 Extreme on the way and a really powerful "Delta" 120mm fan for it (Which took a chunk out of my finger in testing) so I plan on trying to crank up this processor pretty well.

Anyway, on to my question

What I'm seeing is essentially that people are getting the Q6600s up to 400mhz bus speed, with 1600mhz Rated FSB.

I read the RAM 101 topic... and what I gathered is that the best speed will be attained at a 1:1 ratio of RAM/CPU bus speeds.

So if I'm running a Q6600 at 400mhz bus speed, would DDR2-800 be a 1:1 match, since they're both at a 400mhz bus? Or would a 1:1 match be DDR2-1600, hitting 1:1 with the Rated FSB?

Basically, I'm looking at my optimal overclock hitting the 400mhz FSB. I need to know if I can get some good quality DDR2-800 rated sticks or if I should look for something with high overclocking potential.

Right now I'm looking at these:
http://www.overclock.net/hardware/sh...duct/503/cat/9
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post #2 of 4
Quote:
Originally Posted by ProdigySim View Post

I read the RAM 101 topic... and what I gathered is that the best speed will be attained at a 1:1 ratio of RAM/CPU bus speeds.

So if I'm running a Q6600 at 400mhz bus speed, would DDR2-800 be a 1:1 match, since they're both at a 400mhz bus? Or would a 1:1 match be DDR2-1600, hitting 1:1 with the Rated FSB?
DDR2-800 is all you need for 1:1 operation you were right. In certain BIOS (like the EVGA 680i for instance) the 1:1 option is actually 1:2. What you want in that case is Linked -> Sync Mode not 1:1.

There is some people who get better performance from very highly clocked memory but I get better perf from 1:1 (synced) low latency and 1T CMD rate. At the same time it let me run my memory voltage a lot lower than high Mhz preserving it's life at the same time.

A few good kits for the price (I know there are other good kits but this is just price vs performance ratio with prices going on at the time of posting...) -
http://www.newegg.com/Product/Produc...82E16820227231 85$ after rebate 1T EPP
http://www.newegg.com/Product/Produc...82E16820227179 80$ after rebate 1T EPP
http://www.newegg.com/Product/Produc...82E16820146565 80$ after rebate

If I was buying ram today id get one of those kits. Probably the Reaper or the Titanium. I know the Balistix is nice but I am not after the highest Mhz I like the 1T EPP profile.
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Cerebro
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post #3 of 4
In your case...

Stock:
Q6600 @ 1066 QDR/4 = 266.5 FSB x 9 = 2.4GHz
Front Side Bus (FSB) = 266.5MHz
Quad Data Rate (QDR)= 1066MHz (FSB "Quad Pumped")
Double Data Rate (DDR) = 533MHz

1:1 with a FSB @ 266.5MHz = 533MHz Memory Speed

Overclocked:
Q6600 @ 1600 QDR/4 = 400 FSB x 9 = 3.6GHz
Q6600 @ 1600 QDR/4 = 400 FSB x 8 = 3.2GHz (Dropped Multiplier to 8)
Front Side Bus (FSB) = 400MHz
Quad Data Rate (QDR)= 1600MHz (FSB "Quad Pumped")
Double Data Rate (DDR) = 800MHz

1:1 with a FSB @ 400MHz = 800MHz Memory Speed

Your DDR2-800 will be running at its stock rated speed of 800MHz with a 400MHz FSB and a 1:1 memory ratio. In other words, the memory is running in a 1:1 ratio with the FSB.

With DDR2-800 any FSB increase over 400MHz will begin to overclock the memory when left in a 1:1 ratio. For instance:

420MHz FSB = 840MHz memory speed
450MHz FSB = 900MHz memory speed
500MHz FSB = 1000MHz memory speed

The memory can also be overclocked by leaving the FSB at its stock setting of 266MHz and changing the memory ratio by implementing a divider.

The equation for figuring this would be: Front Side Bus multiplied by the Memory Divider multiplied by the Data Rate. The memory runs at double data rate so we multiply by two.

266.5MHz x 1.00 x 2 = DDR2-533 in a 1:1 ratio.

266.5MHz x 1.25 x 2 = DDR2-667 (rounded from 666.25) in a 4:5 ratio.

266.5MHz x 1.50 x 2 = DDR2-800 (rounded from 799.5) in a 2:3 ratio.

266.5MHz x 2.00 x 2 = DDR2-1066 in a 1:2 ratio.

The above memory ratios can be explained as follows:

1:1 = 1 divided by 1 = 1.00

4:5 = 5 divided by 4 = 1.25

2:3 = 3 divided by 2 = 1.50

1:2 = 2 divided by 1 = 2.00

Hope this helps...
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uoıʇnloʌ3
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post #4 of 4
Thread Starter 
Yes, that was actually INCREDIBLY helpful, both responses.

I too have noticed in the past huge performance increases from 1T timings.

I think I'll get those Reapers you linked to and see if I end up sending my RAM past the 400mhz bus.
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main pc
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CPUMotherboardGraphicsRAM
Intel Core i5 2500K P8Z68-V AMD Radeon HD 7800 Series G.Skill 
RAMRAMRAMHard Drive
G.Skill G.Skill G.Skill samsung HD155UI 
CoolingMonitorKeyboardPower
Corsair H60 Acer 120hz Daskeyboard Ultimate Silent (browns) Seasonic 750 modular 
CaseMouseMouse PadAudio
Antec P180 Logitech G700 Mionix Propus 380 Steelseries Siberia v2 
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Sennheiser HD558 
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