Ram speed to cpu fsb ratio help!

[Shadow of Dawn]

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.

 

[Andrius]

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

 

[Shadow of Dawn]

Ok, thanks alot.

 

[DiscoDuck]

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.

 

[Shadow of Dawn]

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?

 

[Andrius]

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).

 

[Shadow of Dawn]

Ok, I'll go check.

 

[Shadow of Dawn]

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

 

[Andrius]

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

 

[Shadow of Dawn]

Sweet!

thanks for the help.

 

[Andrius]

No problem.
Here's some guide I found while checking. It should help you get started on the basics if you need it.
http://www.overclock.net/intel-motherboards/328951-my-750i-ftw-overclocking-guide.html

 

[Shadow703793]

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?

 

[Andrius]

^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.

 

[Shadow703793]

^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.

 

[Andrius]

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.