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 Post subject: Question: FSB OC - 1:1 vs 15:16, which is better?
PostPosted: Sun Aug 07, 2011 4:49 pm 
Coppermine
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As my computer ages more and I don't have the money to upgrade yet, I'm trying to squeeze as much out of it as I can.

Lately I've been running a Core 2 Duo E6600 2.4GHz @ 3.0GHz w/ 1500MHz FSB
I'm running on an MSI P6N SLI mobo.
Patriot DDR2 PC6400RAM (800mhz)

I've been reading from so many people that they are able to get much higher clocks than 3GHz from this processor. However, when I increase my CPU bus speed to more than 375x8 with a 1:1 RAM ratio I freeze in POST. At 375x8 I'm very stable. At 1:1 with the RAM, it makes the RAM run at 750mhz even though its rated for 800MHz. When I set my FSB to 1600 to make my RAM run at 800MHz, it wont POST, even if I lower the CPU multiplier to x7.

I have 2 questions.

1) Are there FSB limits on the motherboard regardless of CPU clock speed, and if so what exactly are the limiting factors? Voltage?
1a) Does anyone happen to know what typical limits may be for an MSI P6N SLI for FSB limits?

2)Is there any performance difference whatsoever in any circumstance between running 375x8 bus @ 1:1 for 750MHz RAM vs 375x8 bus @ 15:16 for 800MHz RAM


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 Post subject: Re: Question: FSB OC - 1:1 vs 15:16, which is better?
PostPosted: Sun Aug 07, 2011 8:00 pm 
Boy in Black
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1:1 is usually best as a rule of thumb, usually shows some actual performance gains, but it's OK to dive under it (like 750 vise 800) in order to achieve a higher CPU clock.

What you may be running into could be one of two things. The one I'd bring up the first in order to dismiss the first, is that the pair of memory sticks you have don't like being behind an OC'd CPU and run 1:1. Patriot is fair memory and should handle all that data pumped through it at least at 400Mhz. The second is what I'd rather point the finger at: That 650i chip, in general, was a bane of my trials at one time. I heard good things (not spectacular, but good for the price) and none of very few I tried actually fared well on OC'ing C2D's. I went through a few XFX Ultra's and one P5N-E before just putting them on the folding pastures. The 6420 did very well in them (2.1Ghz+700Mhz) by just playing with the CPU and memory, but it took more juice on the chip to get to anything more impressive.

So that's what I'd say to try as a valid shot...maybe 1.4v to the NB, but watch for drive corruption as I ended causing a lot of bad blocks on some Raptors while over 3Ghz on that thing (and thus, me giving up on those boards).

A1) I'm not sure how to answer. Sure there's hard limits on FSB, but the way I envision it is what choices you have in any given BIOS. Otherwise, there's typical/theoretical limits on FSB given what chip and board you use as well though that just need found through trial and asking others on their experience just like this. While there may be a setting in a board's BIOS may not mean it's known to do well with it set.
A1a) Nope...never used an MSI 650i board.
A2) This goes back to CPU overclocking mentioned above. Would there be a difference between 375 or 400FSB given the relatively same CPU core speed? Not enough from my memory. The higher core speeds attained did a lot more in the end than some perceived bandwidth lost from dropping the ratios. HOWEVER, there were some ratios that just did play well with the system as a whole, and I believe 15:16 was one I did not like at all. I just tried to search, but can't find that endeavor. If you can get that thing to 3.2Ghz even with a 333Mhz range FSB/Ratio, I'd say you're better off going that route.

(It's been a while, but does 5:4 sound like an available option? Just bringing it up for no other purpose than it sticking out in mind currently)


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 Post subject: Re: Question: FSB OC - 1:1 vs 15:16, which is better?
PostPosted: Mon Aug 08, 2011 10:59 am 
Coppermine
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Isn't 5:4 saying the cpu bus is greater than the ram speed thus bottlenecking fsb? I juat read here that at stock speed 4:5 is better than 1:1 though. Not sure if that holds true at other speeds.

http://www.yougamers.com/forum/showthread.php?t=65718

My stock NB voltage is 1.25v and has a passive stock cooler (no fan). Is 1.4v safe? Not used to messing with NB voltage. I'm currently at 1.4 on my cpu but it drops to ~1.376v when I run a p95 blend torture. Temps are peaking at 67C on the fft 8k iteration though. They drop down to 63ish though during the same iteration, jumping around in between during the 8k's.

It also seems like from what I read people have had mpre success OCing with the 680 board and I did see one post about someone else with an fsb limit on my board in the low 1500s. Didn't find overwhelming evidence that 650s were bad at ocing c2d's but I'll have to look again to see what kind of numbers people were getting with the mobo.

Lastly, theoretically would 3.2ghz at 1424 fsb be better than 3.0ghz aat 1500 and would it depend on what type of application I'm usually running?


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