Is the overclocking guide correct?

Isaac MM

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Apr 13, 2007
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Originally posted by: graysky

DDR3-1333 (PC3-10666) 9-9-9-24
DDR3-1600 (PC3-12800) 7-7-7-20

? The first part is self-explanatory (DDR3 memory).
? The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you?re lucky).
? The PC3-XXXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR3-xxxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 32 (rounded in some cases). Example using a 400 MHz FSB: 400x32=12800. So you?d need at least PC3-12800 to run on FSB of 400 MHz.

I thought a 1600mhz ddr3 ram allowed systems to run with a FSB of up to 800mhz?
 

graysky

Senior member
Mar 8, 2007
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To the best of my knowledge, what I've written is accurate.... which modern motherboard allows you to use a FSB of 800 MHz?
 
Nov 26, 2005
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It is correct!

The ratio on DDR3 1600 with a fsb of 800 is a ratio of 1:2
Its 1:1 on a DDR2 800 system. There isn't any bios 800 fsb frequency ...yet.

EDIT: don't forget the DDR whether 1,2,3,4,5 and so on is double the data rate!
 

n7

Elite Member
Jan 4, 2004
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No it is not correct.

Technically the lowest you can generally run is 1:1, even for DDR3 on most mobos.

So that's not accurate actually.

The OP is correct in stating that if you have DDR3-1600, 1:1 would be 800 MHz.
While impossible, it's theoretically true.

graysky, your calculations are based around the 1:2 ratio for DDR3.

While that is indeed ideal for DDR3, you do not have to run 1:2.
You can certainly run lower ratios.

For a stock 333 MHz FSB DDR3 system, lowest speed would be 1:1 DDR3-667 (horrible idea, but doable).
For a stock 333 MHz FSB DDR3 system, ideal (but not mandatory) speed would be 1:2 DDR3-1333.

Here are some common DDR3 ratios (taken from this review):
1:1, 6:5, 5:4, 4:3, 3:2, 8:5, 5:3, and 2:1 (dependent upon strap selection)

So that gives a whole lotta options.

Assuming a 333 MHz FSB CPU, that gives:
1:1 - DDR3-667
5:6 - DDR3-800
4:5 - DDR3-833
3:4 - DDR3-889
2:3 - DDR3-1000
5:8 - DDR3-1066
3:5 - DDR3-1111
1:2 - DDR3-1333

So for those systems running a higher FSB like 500 MHz, you can use the 5:8 ratio for DDR3-1600, e.g.
Or say someone has their Q9450 @ 8x450, but has RAM that cannot do much over DDR3-1333, they could run 2:3 for DDR3-1350.

Now this all gets tricky due to straps & tRD, etc, but there are many options for speeds with DDR3.
And unlike the DDR/DDR2 days where most people ran 1:1, 1:1 is the worst possible speed with DDR3...1:2 is what will always be strived for, unless they allow an even higher ratio.
 
Nov 26, 2005
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Originally posted by: BTRY B 529th FA BN
It is correct!

The ratio on DDR3 1600 with a fsb of 800 is a ratio of 1:2
Its 1:1 on a DDR2 800 system. There isn't any bios 800 fsb frequency ...yet.

EDIT: don't forget the DDR whether 1,2,3,4,5 and so on is double the data rate!

It is correct!

The ratio on DDR3 1600 with *DRAM* frequency of 800 is a ratio of 1:2
Its 1:1 on a DDR2 800 system. There isn't any bios 800 fsb frequency ...yet.

EDIT: don't forget the DDR whether 1,2,3,4,5 and so on is double the data rate!


EDIT: don't mess with the Zohan :)

EDIT2: 800 fsb frequency through the bios is unheard of
 

n7

Elite Member
Jan 4, 2004
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Originally posted by: BTRY B 529th FA BN
The ratio on DDR3 1600 with a fsb of 800 is a ratio of 1:2
Its 1:1 on a DDR2 800 system. There isn't any bios 800 fsb frequency ...yet.

Incorrect.
DDR3-1600 / 2 = 800 MHz.
800 MHz FSB = 800 MHz RAM = 1:1, not 1:2

Correct.
DDR2-800 / 2 = 400 MHz
400 MHz FSB = 400 MHz RAM = 1:1, yes.



? The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you?re lucky).

This is incorrect.

The lowest possible ratio for DDR3 is 1:1.

1:1 means same speed RAM as the FSB.

If the FSB is 400 MHz (1600 MHz quad pumped), then 1:1 RAM is 400 MHz, aka DDR3-800!
DDR3-1600 is NOT required, as that is 1:2.

The OP, Isaac MM, mentions [though it only applies in theory] that DDR3-1600 would actually allow a FSB of 800 MHs, not a FSB of 400 MHz.
He is correct, though it is not possible.

Basically, graysky's guide states 1:2 is the lowest ratio available for DDR3, which is incorrect.
As i mentioned, it's the ideal ratio, yes.
But it's NOT the minimum; please see my post above for the available DDR3 ratios.
 

OCGuy

Lifer
Jul 12, 2000
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Originally posted by: BTRY B 529th FA BN
DRAM @ 800 with DDR3 1600 IS 1:2 RATIO not a fsb frequency of 800

I think you are confused.


400FSB with 800mhz RAM is 1:1...not 1:2.

800FSB with 1600mhz RAM would be 1:1
 

taltamir

Lifer
Mar 21, 2004
13,576
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Nice insights, but not really addressing the original question.

I thought a 1600mhz ddr3 ram allowed systems to run with a FSB of up to 800mhz?"
DDR stands for "Double data rate" memory. There are multiplications of the base FSB. Actually DDR3 would be better presented as DDR to the third power. The actual cells are running at 200mhz, and then they are doubled to 400mhz (DDR), doubled again to 800 (DDR2), and doubled again for 1600mhz (DDR3).
There are also base cells @ 133mhz and 166mhz... which go through the same triple doubling.

Different places will refer to it in different ways though. With the unmultiplied (or partially multiplied) amount being referred to as "base" speed.
 

graysky

Senior member
Mar 8, 2007
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I'm confused... the wording I chose in the guide is "The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you?re lucky)."

I believe it reads correctly as such sine the max. divider is 1:2, no? Please correct me if I'm mistaken or if I'm not understanding.
 

n7

Elite Member
Jan 4, 2004
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I need to re-iterate what i said about 1:2 being max ratio for DDR3.

It seems nVidia's 790i chipset does even higher than 1:2 :D
But 1:2 is still highest for Intel chipsets.

I really wish i had a DDR3 system so i could screenshot what i am trying to explain.

The actual ratios available will depend on the strap used, so not every board is going to have all the ratios i listed earlier, but those are what could be available on most boards, & should be on most higher end boards.

graysky, you're calculating maximum FSB based on a RAM ratio of 1:2, but as i've tried to explain, one does not have to run 1:2, there will usually be lower available ratios.

It's like stating you can't run anything lower than DDR2-1066 on a 266 MHz FSB CPU...you disagree with that, right?
That's what you're saying for DDR3, except that's not the case.

Someone with DDR3 please come in here & post your available RAM ratios w/ CPU-Z screenies...i give up trying to explain this.

BTW, i absolutely agree 1:2 is an ideal ratio for DDR3.
But it's not usually the minimum one though.

 

n7

Elite Member
Jan 4, 2004
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Originally posted by: BTRY B 529th FA BN
DDR3 DRAM freq option 800

Bingo!

Finally.

This is the entire point i have trying to make from my first post!

See how BTRY B 529th FA BN has his DDR3 running @ DDR3-800 1:1


That is the lowest you can do for DDR3, just like for DDR2.

You do NOT need DDR3-1600 minimum for FSB @ 400 MHz.
DDR3-800 is all that's technically needed to run a 400 Mhz FSB with DDR3, as that screenshot shows.

It's exactly the same as with DDR2.
Except that with DDR3, we have much higher speeds than we do with DDR2, so it's not ideal. However it is possible!

So while with DDR2 it makes sense to run 1:1 (or slightly higher if possible), it makes absolutely no sense to do so with DDR3.

I hope this finally sinks in...

Thanx for the screenie BTRY B 529th FA BN, muchly appreciated.



 

JustaGeek

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Jan 27, 2007
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Graysky is absolutely correct. Here is another look at the divider/multipliers/ratios, based on "basic" FSB speed. I wrote it a few months back for another purpose, but will try to edit it for the 1600 MHz RAM.

The "basic" FSB speed is 266.6MHz, or 333MHz, or 400MHz.

That's where it all starts, and everything revolves around that.

CPU
266 FSB x 9 multiplier = 2.4GHz E6600 speed
333 FSB x 9 multiplier = 3.0 GHz E6850 speed
200 FSB x 11 multiplier = 2.2GHz E4500 speed

"Quad pumped" FSB
266 FSB x 4 = 1066 MHz "Quad pumped" E6600 FSB
333 FSB x 4 = 1333 MHz "Quad pumped" E6850 FSB
200 FSB x 4 = 800 MHz "Quad pumped" E4500 FSB

Memory bus/Memory speed.

266 FSB x 3:2 Memory Multiplier = 400 MHz Memory Bus x 2 DDR = 800 MHz Memory Speed
333 FSB x 6:5 Memory Multiplier = 400 MHz Memory Bus x 2 DDR = 800 MHz Memory Speed.
400 FSB x 2:1 Memory Multiplier = 800 MHz Memory Bus x 2 DDR = 1600 MHz Memory Speed.

Going backwords, the 1600:4 = 400MHz FSB is correct.
 

n7

Elite Member
Jan 4, 2004
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HTF can you guys not get this?! :confused:

? The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you?re lucky).
? The PC3-XXXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR3-xxxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 32 (rounded in some cases). Example using a 400 MHz FSB: 400x32=12800. So you?d need at least PC3-12800 to run on FSB of 400 MHz.

How about this, if this is correct, please explain how we can have a FSB @ 400 with RAM @ 400 (DDR3-800).
http://i3.photobucket.com/albu...88/529th/11drambus.jpg
Please look at that screenshot.
Based on those calculations & screenshot, explain how 800 / 4 = 400, or how 6400 / 32 = 400.

How about this one line:
So you?d need at least PC3-12800 to run on FSB of 400 MHz.
So how exactly is BTRY B 529th FA BN running FSB of 400 with PC3-6400.

*bangs head on desk*
 

JustaGeek

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Jan 27, 2007
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Originally posted by: n7
HTF can you guys not get this?! :confused:

? The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you?re lucky).
? The PC3-XXXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR3-xxxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 32 (rounded in some cases). Example using a 400 MHz FSB: 400x32=12800. So you?d need at least PC3-12800 to run on FSB of 400 MHz.

How about this, if this is correct, please explain how we can have a FSB @ 400 with RAM @ 400 (DDR3-800).
http://i3.photobucket.com/albu.../529th/busdram9300.jpg

Based on those calculations, explain how 800 / 4 = 400, or how 6400 / 4 = 400.

*bangs head on desk*

Nobody is dividing the 800 by 4. 800 is divided by 2, since the FSB/Memory Bus ratio is 1:1.

YES, it is possible to run the DDR3 1600 at only 800MHz, as it is possible to run the DDR2 800 at only 400MHz, with the FSB of 200MHz and 1:1.

It just doesn't make sense, does it...?

All graysky stated in his thread is that the 1600MHz DDR3 RAM requires the FSB of 400MHz - obviously this will require the FSB:Memory Bus ratio of 1:2, but that wasn't his point.

You can underclock practically any RAM, and you can underclock the 1600MHz DDR3 to 800MHz.

But why would you want to do that, buying the expensive DDR3...? :confused:

 

n7

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Jan 4, 2004
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Of course you wouldn't want to do that; i've stated that countless times in this thread already.

My point (& the OP's) is that the guide states you need DDR3 RAM capable of running a FSB:RAM ratio of 1:2, which is not correct.

I am not saying running any of the following lower ratios is better:
(Based off a 333 MHz FSB)
1:1 - DDR3-667
5:6 - DDR3-800
4:5 - DDR3-833
3:4 - DDR3-889
2:3 - DDR3-1000
5:8 - DDR3-1066
3:5 - DDR3-1111

I am simply saying it's possible, just like the OP stated.

Sorry to get a little frustrated, but i cannot figure out how it's taken this long for that to be comprehended.

 

JustaGeek

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Jan 27, 2007
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Originally posted by: n7
.
Based on those calculations & screenshot, explain how 800 / 4 = 400, or how 6400 / 32 = 400.

Why are you dividing the 6400 MB/s, which is the bandwidth, by 32, to get 400MHz...?

This is mathematically impossible, unless you are trying to say something else here...

:confused:
 

JustaGeek

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Jan 27, 2007
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Originally posted by: n7
Of course you wouldn't want to do that; i've stated that countless times in this thread already.

My point (& the OP's) is that the guide states you need DDR3 RAM capable of running a FSB:RAM ratio of 1:2, which is not correct.

I am not saying running any of the following lower ratios is better:
(Based off a 333 MHz FSB)
1:1 - DDR3-667
5:6 - DDR3-800
4:5 - DDR3-833
3:4 - DDR3-889
2:3 - DDR3-1000
5:8 - DDR3-1066
3:5 - DDR3-1111

I am simply saying it's possible, just like the OP stated.

Sorry to get a little frustrated, but i cannot figure out how it's taken this long for that to be comprehended.

Of course it is possible, but thats why we use the less expensive DDR2 at the speeds you mentioned above.

If you spend your money on 1600MHz DDR3, you want it to run at its full capabilities, which is 1600MHz, requiring the FSB of 400MHz. Unless you can get the Memory Bus Multiplier higher than 2 - are there motherboards like that available...?

 

JustaGeek

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Jan 27, 2007
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OK, trying to understand the semantics here, I get the n7's point.

You can actually run the 1600MHz DDR3 with the FSB higher that 400MHz, using the proper memory multiplier.

500MHz FSB x 1.6 Memory Multiplier = 800MHz Memory Bus x 2 DDR = 1600MHz.

Yes, n7 is correct - 400MHz is not necessarily the maximum FSB for DDR3 1600.
 
Nov 26, 2005
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As far as I know and correct me if I am wrong:

bus = 133, 266, 333, 400 and its given that they can be manipulated lower or higher giving different results to total CPU speed for locked multipliers.
With DDR, the bus is always doubled cause its double the data rate. What ever memory you buy be it DDR, DDR2, DDR3, etc. the number (i usually use "number" e.g. DDR(X) [number]) is the final number the (bus speed x 2) is divided into, hence the ratio.

Is this wrong?