FSB:Dram ratio please explain to me

[huntsman]

Ok so Iv been reading for a while now but I still dont understand this. Also what is a memory divider is that an actual setting in my bios? I read about it and I dont get what the memory divider is either.

Lets talk about the ratio first. Iv seen examples that other people posted but it would help me out the most if I used my specs. So i have an fx8320 3.5ghz fsb at 200mhz also have ddr3 1600mhz

cpu-z shows fsb:dram 1:4 ratio.

I understand that ddr is double rate so 1600mhz = 800mhz.

Mine is running at 802mhz and fsb at 200mhz. So 802/200 = 4.01 I kinda get where the 1:4 ratio is coming from. What I dont understand is how do you get a 1:1 ratio ? Seems like my fsb would have to be 800mhz or I could get a 1:2 ratio if my fsb was 400mhz ?? im super confused and frustrated.

or would I have to lower my rams mhz to achieve a 1:1 ratio ? If somebody can explain this to me it would make my night cuz its bothering me haha.

 

[SchizTech]

Why do you want to change the ratio? As long as the RAM performance is good you'll run well but messing with the base clock (fsb) is tricky

 

[huntsman]

Well its not that I want to change it. I just want to understand it.

 

[Pinhedd]

Ok so Iv been reading for a while now but I still dont understand this. Also what is a memory divider is that an actual setting in my bios? I read about it and I dont get what the memory divider is either.

Lets talk about the ratio first. Iv seen examples that other people posted but it would help me out the most if I used my specs. So i have an fx8320 3.5ghz fsb at 200mhz also have ddr3 1600mhz

cpu-z shows fsb:dram 1:4 ratio.

I understand that ddr is double rate so 1600mhz = 800mhz.

Mine is running at 802mhz and fsb at 200mhz. So 802/200 = 4.01 I kinda get where the 1:4 ratio is coming from. What I dont understand is how do you get a 1:1 ratio ? Seems like my fsb would have to be 800mhz or I could get a 1:2 ratio if my fsb was 400mhz ?? im super confused and frustrated.

or would I have to lower my rams mhz to achieve a 1:1 ratio ? If somebody can explain this to me it would make my night cuz its bothering me haha.

Your understanding is pretty much correct. The FSB😀RAM ratio is the ratio between the clock frequency of the FSB and the clock frequency of the DRAM.

The FSB is QDR, or Quad-Data-Rate. It transfers data four times per cycle, so a 200Mhz FSB results in 800 MT/s across the Front Side Bus.

DDR SDRAM is DDR, or Double-Data-Rate. It transfers data two times per cycle, so a 400Mhz DDR-SDRAM results in 800 MT/s across the DRAM IO Bus (a channel).

DDR3-1600 necessarily has an 800Mhz clock. This is derived from the FSB using the FSB😀RAM ratio. A 1:4 ratio means that the DRAM clock is 4x faster than the FSB clock. This clock multiplication is accomplished using a PLL, or Phase-Locked-Loop.

A source clock signal is fed into the PLL, and one or more derived clocks can be generated. One of the clocks outputs will be the source clock that was fed in, and all other clocks outputs may be some multiple of this source clock. The PLL can both multiply and divide the clock (which allows for fractional ratios such as 2:3 which multiplies by 3 and divides by 2 to yield 1.5) as well as adjust the phase of derived clocks relative to the source clock.

In most motherboards, an oscillator (either a crystal oscillator, or a voltage controlled oscillator) is used to drive a Schmitt trigger, which in turn drives a clock buffer, and the output of this clock buffer is used as the source for the PLL. In many cases, this is all integrated into one chip.

That's a bit of a lengthy explanation, but it hits the important points. What I don't understand though is why you're trying to obtain a 1:1 ratio. To do so, you would have to crank your FSB all the way up to 800Mhz (which is absurd) or downlock your memory to 200Mhz, which is below the minimum supported by DDR3. There is no benefit to a 1:1 ratio, this is just a rumor that's been floating around the internet for at least the past decade.

 

[huntsman]

Thanks, I was missing the part that the fsb is quad data rate. I didint know that. Im not trying to obtain a 1;1 ratio. I just want to learn about all these different settings and how they effect each other. From my understanding the 1;1 ratio was used back in the day, and it does not matter anymore as the cpu has integrated memory controllers now.

The reason I was asking is because like you said to get a 1;1 ratio my FSB would have to be 800mhz and that sounded ridiculous to me. I thought I might have missed something and was thinking it the wrong way. Seems like with DDR and maybe DDR2 you could achieve the 1;1 ratio as they ran at lower mhz.

Thanks for clearing it up for me.

 

[Pinhedd]

Thanks, I was missing the part that the fsb is quad data rate. I didint know that. Im not trying to obtain a 1;1 ratio. I just want to learn about all these different settings and how they effect each other. From my understanding the 1;1 ratio was used back in the day, and it does not matter anymore as the cpu has integrated memory controllers now.

The reason I was asking is because like you said to get a 1;1 ratio my FSB would have to be 800mhz and that sounded ridiculous to me. I thought I might have missed something and was thinking it the wrong way. Seems like with DDR and maybe DDR2 you could achieve the 1;1 ratio as they ran at lower mhz.

Thanks for clearing it up for me.

Indeed with DDR and DDR2 the ratios were much lower.

DDR-400 (PC-3200, 200Mhz) was commonly used with second and third generation Pentium 4 microprocessors. Third generation Pentium 4 microprocessors supported a 200Mhz FSB (same 800 MT/s as described above). Thus, a 1:1 ratio was normal.

DDR2-800 (PC2-6400, 400Mhz) was commonly used with first and second generation Core 2 microprocessors. Most of these motherboards and microprocessors called for 266Mhz FSB or 333Mhz FSB which would result in a 1:1 ratio when used with DDR2-533 or DDR2-667 respectively. High end Core 2 motherboards could easily hit a 400Mhz FSB and this was a common value for overclocking and would make a good 1:1 ratio when used with DDR2-800. One microprocessor was actually specified for a 400Mhz FSB (QX9770) so again, a 1:1 ratio was not unreasonable.