Half Multipliers on Core 2

[canis]

Are half multipliers less stable than full multipliers on Core 2? Stable in terms of OC ability. Is half multipliers a recent introduction from pentium III onwards?

 

[VirtualLarry]

I think the Pentium MMX had half-multis too, but more recently, the Core2 series added half multis. I don't think that they are any less stable than full multies.

 

[canis]

How do the dividers line up with half multipliers?

 

[Spikesoldier]

half multipliers are only on the 45nm C2D's IIRC.

shouldnt worry about the multiplier being a half value, as multiplier only effects the clock speed of the chip itself and not any bus speeds or memory speeds.

i really wouldnt worry about it at all.

 

[aigomorla]

no no no dont use half multis.

Because it rounds your ram multi up.

If you dont have extremely high performance ram, that can be a killer having the multi rounded up.

 

[Borealis7]

i'm sorry to question the great Aigomorla...but what does it have to do with RAM multis?

for instance, if you have a wolfdale @ 1333 Mhz FSB quad pumped = 333MHz FSB, you set the bios to run at 400MHz FSB and set your ram to 1:1, then your 800MHz DDR2 actually runs at 800 MHz.

so what does it matter if your CPU has a half multiplyer?

 

[n7]

It has nothing to do with RAM.

No idea what aigo is talking about.

 

[aigomorla]

i'm sorry to question the great Aigomorla...but what does it have to do with RAM multis?

for instance, if you have a wolfdale @ 1333 Mhz FSB quad pumped = 333MHz FSB, you set the bios to run at 400MHz FSB and set your ram to 1:1, then your 800MHz DDR2 actually runs at 800 MHz.

so what does it matter if your CPU has a half multiplyer?

Oh im sorry i got backwards. The ram rounds down, and not up.

If your running 7.5x multi, your ram will be running as if your cpu was set at the 7x multi. Which will require a higher ram speed.

So while your cpu has a multi of 7.5 your ram will be running on a multi of 7x, which will require your ram to be run higher to = target fsb speed of your cpu.

I remember running into this problem on the lower end multi cpu's, when pumping your fsb over 333.

If you already have a high end multi it wont matter, but rember the highest multi your looking at on your setup with a half multi is a 9.5x.

If i remember correctly.

Just use the real multi, and avoid using the half multi for the ram reasons unless your multi is high to begin with.

for instance, if you have a wolfdale @ 1333 Mhz FSB quad pumped = 333MHz FSB, you set the bios to run at 400MHz FSB and set your ram to 1:1, then your 800MHz DDR2 actually runs at 800 MHz.

so what does it matter if your CPU has a half multiplyer?

No you caught me on a messup, the multi rounds down.
Sometimes even with the divider, if you use that rounded down multi, you will be shorted, becuase your divider is based on keeping the FSB and Memory multi the same.

But as i said, when you use a half multi, the multiplier for the ram rounds down.

As i said we would need to see what half multi u were thinking about using.
But the X3380 i believe was a 9.5multi quadcore and the highest one u could get.

If this is an i7 with a 21x multi, then the half multi doesnt do much.

But on a LGA775 with a max multi of 9.5x... im assuming your running a 8.5x or lower, that .5 multi hurts as the multi gets smaller.

It has nothing to do with RAM.

No idea what aigo is talking about.

RAWR u know what im talking about...
remember on the E6X50's which used a half multi, you would find out u were very ram speed limited quickly, because of the half multi and the 1333fsb or 1600fsb.

 

[bobross419]

Oh im sorry i got backwards. The ram rounds down, and not up.
snip

RAWR u know what im talking about...
remember on the E6X50's which used a half multi, you would find out u were very ram speed limited quickly, because of the half multi and the 1333fsb or 1600fsb.

Is there anyone other than aigo that can confirm this? Not that he isn't godly in this sort of thing (And I'm going to do some searches after I post this) , but if this is accurate it could be why I can't overclock my Q9550 with generic Dell DDR2 800 RAM.

 

[VirtualLarry]

I dunno, Aigo, I think that you are still thinking of the i7 and friends. On the C2Ds, multi has nothing to do with RAM speed. RAM speed is a combination of the FSB and the system chipset's RAM multi. As long as you FSB and RAM divider remain constant, it shouldn't matter what the multi is. At least in theory.

 

[extra]

Multiplier on C2D chips has nothign to do with RAM speed lol... Yea

 

[bobross419]

Alright, I did some searching and couldn't find anything about this. Here are the closest threads I could find:

http://forums.anandtech.com/showpost.php?p=23300270&postcount=12
http://forums.anandtech.com/showthread.php?t=96404&highlight=half+multiplier
http://forums.anandtech.com/showthread.php?p=28340113#post28340113

Couldn't find anything on Google about this either

 

[aigomorla]

I dunno, Aigo, I think that you are still thinking of the i7 and friends. On the C2Ds, multi has nothing to do with RAM speed. RAM speed is a combination of the FSB and the system chipset's RAM multi. As long as you FSB and RAM divider remain constant, it shouldn't matter what the multi is. At least in theory.

Yeah i know what your saying.. but im telling you those .5 multis works differently.

Alright, I did some searching and couldn't find anything about this. Here are the closest threads I could find:

http://forums.anandtech.com/showpost.php?p=23300270&postcount=12

Couldn't find anything on Google about this either

Ugh... i wish i had the link in XS Which showed this.

in a typical 1:1 setup 400mhz on fsb should be 400mhz on the ram.
With the .5 multi this isnt so, which is why i always avoided that .5 multi when overclocking.

Thats why the boards dont let you type in a .5 multi unless they changed that too, instead you would set your multi, and put in the option of .5 as yes.

Dayam... wish gillbot was here to back me up, because he had a simular issue first hand.

Which is why we always said that .5 multi was intel's way of dicking us around.

But as i said, when i was playing with cpu's with .5 multi, this was the rule i learned on XS.

How about someone test it? a CPU-Z is all it would take. And if im wrong... then i guess im wrong. :T

EDIT: I just asked my friend and he doesnt even remember either if im right or wrong.. can someone just test it?
I dont have a half multi LGA775 cpu anymore.

 

[Gillbot]

Yeah i know what your saying.. but im telling you those .5 multis works differently.



Ugh... i wish i had the link in XS Which showed this.

in a typical 1:1 setup 400mhz on fsb should be 400mhz on the ram.
With the .5 multi this isnt so, which is why i always avoided that .5 multi when overclocking.

Thats why the boards dont let you type in a .5 multi unless they changed that too, instead you would set your multi, and put in the option of .5 as yes.

Dayam... wish gillbot was here to back me up, because he had a simular issue first hand.

Which is why we always said that .5 multi was intel's way of dicking us around.

But as i said, when i was playing with cpu's with .5 multi, this was the rule i learned on XS.

How about someone test it? a CPU-Z is all it would take. And if im wrong... then i guess im wrong. :T

EDIT: I just asked my friend and he doesnt even remember either if im right or wrong.. can someone just test it?
I dont have a half multi LGA775 cpu anymore.

I don't recall the specifics, but I stopped using the .5 multis because they were a pain and caused instability for me and quite a few others.

 

[n7]

I have no idea what you are talking about aigo

Never heard of a half-multi having any effect on RAM speeds for Core 2s.
RAM frequencies on LGA775 are entirely derived from the FSB speed; nothing to do with the CPU multi.

I've done a LOT of playing with RAM dividers on LGA775 & have never heard or seen what you are mentioning.

Some old skool 8.5x multi screenshots.

 

[aigomorla]

I have no idea what you are talking about aigo

Never heard of a half-multi having any effect on RAM speeds for Core 2s.
RAM frequencies on LGA775 are entirely derived from the FSB speed; nothing to do with the CPU multi.

I've done a LOT of playing with RAM dividers on LGA775 & have never heard or seen what you are mentioning.

Some old skool 8.5x multi screenshots.

mmmm i guess i was wrong.. :\