# Ram speed to cpu fsb ratio help!

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I will be building a new computer soon and I’m going to get a Q9450 and some 2x2gb G-Skill ddr2 1000, and I don’t plan to overclock at first. Anyways, I read somewhere that I can run the ram at 1000mhz and the cpu fsb at 1333mhz at a 2:3 ratio. Is this true? I am confused about this.

Also I will be using a Evga 750i FTW motherboard.

Help is very much appreciated.

1. CPU FSB is "quad pumped". The physical frequency is 333MHz. The data rate is 1333MHz.

2. Intel's memory controller uses a dual channel double data rate layout.
To match (a ratio of 1:1) the Q9450's FSB of 1333MHz (QP) you need 667MHz DDR2 memory.

3. Your 1000MHz DDR2 runs at a physical frequency of 500MHz. So this would mean a ratio of 333MHz:500MHz or 2:3 like you said.

The short version for the 2:3 ratio
FSB : 333MHz x4(QP) = 1333MHz data rate
RAM : 500MHz x2(DDR) x2(DC) = 2000MHz data rate

Ok, thanks alot.
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I dont know about bios ratios but the math doesnt work for 1000/1333 to equal 2/3. According to my calculator a 3/5 would work at 800/1333, if that setting exists. If you dont plan to overclock, get motherboard approved ram and let it run at default spd timings.

From what Andrius said, the ram is in duel channel mode so its actually 2000mhz. So its 1333/2000 which is 2:3

Also how do I close this thread, or can you not close threads?

You don't need to close it AFAIK. Someone will resurect it in 6-8 months and a moderator will kill it after that.

About the ratios : It depends on the manufacturer.
Gigabyte uses : 2.0, 2.4, 3.0 and the likes. So 333 x 2.4 = 800 (DDR)
Asus uses : 2:3, 3:5, 5:8 and so on. So 333:400 = 5:6, 333:500 = 2:3
Some motherboards don't support this so read the manual. I'm not sure about the EVGA 750i FTW. You can always get RAM to run at a ratio of 1:1 if it doesn't work otherwise.

@DiscoDuck
The ratios are FSB:RAM. For gigabyte and some others you need to use DDR frequencies. For ASUS you need physical frequencies (half of DDR). Your math doesn't add up because you turned them around.
3:5 works for 200:333 (or your 800:1333) on budget chips (E2xxx) with slower RAM (DDR2 667).

Ok, I'll go check.

I read the manual but couldn't find anything that says it can run a 2:3 ratio. Maybe I missed something, idk.

I've checked too. EVGA has a FSB:MEM Unlinked option so you can run any frequencies you want to.

Sweet!

thanks for the help.
a b à CPUs

Andrius said:
I've checked too. EVGA has a FSB:MEM Unlinked option so you can run any frequencies you want to.

Correct. Some ASUS boards do this too. I believe the ASUS Formula has this. Not sure about Gigabyte boards though. Also any one know if being able to run at unlinked is related to a perticuler chipset? Can all chipsets do this?

^Gigabyte doesn't have unlinked FSB:MEM (My P35-DS3P board is midrange on the P35 food chain, a friends P35-DS4 doesn't have it either).

Most ASUS boards don't have the unlinked option either. In fact I think only NVIDIA chipset based boards have the Unlinked option. But I could be wrong on this.

a b à CPUs

^Yeah, I took a look at the unlinked RAM option, in deed only high end ASUS boards with nVidia chips seems to have it so far. Would be quite helpful to have it on a P35/X38,etc.

I agree. It's usefull and would be nice to have on all Intel boards.
Or you could buy good quality Geil RAM (like I did). It overclocks to 450MHz(900MHz DDR) at 4-4-4-12 and 1.95V on my DS3P.
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