It looks like the 800 MHz FSB P4's WILL be OK for overclocking

[oldfart]

There was a thead posted awhile back about "The end of overclocking" with 800 MHz FSB P4s. The idea was that @ 800 MHz DDR400 at stock speeds would not leave much room for FSB overclocking without memory problems.

It looks like i875 boards have mem ratios!! Take a look at this post about an AOpen AX4C running a 800 MHz FSB P4 3.0:

And to answer Oldfart's question - yes, the ram can run async. You can enter the cpu FSB in 1 meg increments and then set the mem multiplier to 1.00, 1.33, 1.6, or 2.00
So a fsb of 200 MHz and ram multiplier of 2.00 is 400 DDR. 200 FBS x 1.6 ram multiplier is 320 (it does not do 333). I've tested running the board at 200 fsb and ram @ 266, 320, and 400. Only at 400 DDR did I ahve to increase ram voltage to 2.7 volts. This is with Corsair XMS3200LL matched pair 256 meg modules.

The 1.6 DDR multiplier would allow a P4 3.0 to run 500 Mhz FSB, 3.75 GHz and still be @ DDR400.

The mem ratio feature on an 875/865 board is critical if you plan on overclocking an 800 MHz CPU. It remains to be seen if all board makers will have this. I would make sure it did before I bought one.

 

[jpetermann]

SCHWEET!!!

PJ

 

[DAPUNISHER]

Great info-bump!

 

[oldfart]

It looks like the Abit IC7-G also has the 3:2 and 5:4 ratios. Good news.

 

[THUGSROOK]

oh boy ~ now we have half overclocking!? :Q :disgust:

the Asus also has underclocked mem ratios ~ download the pdf files....

 

[THUGSROOK]

oh and dont forget ~ async mem ratios kinda suck

 

[brucehao]

I always thought the question was whether or not the processors could handle the increased speed. Is it likely to see a 750mhz overclock on a brand new chip? I mean, only the latest 2.4 and 2.53's have enjoyed near 1ghz overclocks.

 

[oldfart]

Originally posted by: THUGSROOK
oh boy ~ now we have half overclocking!? :Q :disgust:

the Asus also has underclocked mem ratios ~ download the pdf files....

So what is wrong with mem ratios? You can still use 1:1 if your ram can handle the speed.
You dont HAVE to use them, but its good that they are there if your FSB speed exceeds your DDR capabilities. You will lose 20% on the mem BW, but its been shown enough times that CPU speed and FSB speed are much more important. You know that. Without the ratios, 800 MHz overclocking would have been very dificult until DDR speeds improve.

Glad to see Asus has them as well. It seems like it will be a common feature.

 

[THUGSROOK]

oldfart ~ i will sit back and watch you guys try this.
my prediction is that the underclocked mem ratios are gonna suck for actual performance.
yea youll get the cpu overclock ~ but it wont be very impressive w/o 1:1 mem ratio.

not to mention an underclocked ratio is a huge comprimise!

 

[Thor86]

Originally posted by: THUGSROOK
oldfart ~ i will sit back and watch you guys try this.
my prediction is that the underclocked mem ratios are gonna suck for actual performance.
yea youll get the cpu overclock ~ but it wont be very impressive w/o 1:1 mem ratio.

not to mention an underclocked ratio is a huge comprimise!

And so it was spoken.

 

[oldfart]

Totally disagree. Look at how little performance increase we got when going to DC DDR over SC DDR with a ratio. Most apps 3 - 5 %. Whoopie.

Lets look at raw numbers here just using a stock 533 MHz FSB as an example. The numbers scale up as well.

533 MHz FSB DC DDR @ 1:1 = 4.2 GB/sec BW
533 MHz FSB SC DDR @ 3:4 ratio = 2.8 GB/sec BW
533 MHz FSB DC DDR @ underclocked .8 ratio. = 3.36 GB/sec BW

The 4.2 and 2.8 mem BW generally perform within 5% of each other. 3.36 GB/Sec would be even less noticeable. Here is the benefit.

An example:
Overclock a P4 3.0 800 MHz FSB CPU to 1 GHz FSB.

With a 1:1 ratio, you would need DDR that could run 500 MHz. No way. Use the 5:4 ratio, DDR400. How about performance? Lets say we used a P4 3.0 800 Mhz FSB. I'm going to say you had really good DDR that could do DDR450.

DC DDR @ 1:1
15 x 225 = 3.375 GHz
DDR450

DC DDR @ 5:4
15 x 250 = 3.75 GHz
DDR400

Which setup is faster? The 3.75 GHz by a mile.

These numbers are examples, but they work. You NEED the mem ratios is you are to do any FSB overclocking on 800 MHz CPUs. Without them, you are limited to ~ a 50 MHz FSB speed increase assuming DDR450 ram quality. That is a pathetic 12.5 % increase in FSB speed.

 

[Spicedaddy]

I'm glad Canterwood motherboards have this feature. We'll be able to OC the "C" chips higher, while still maintaining good mem bandwidth. (and they should overclock well since they'll all be new stepping)

Running the 1.6 multiplier still gives more bandwidth than a single channel setup running in 3:4... At least it gives you an option until DDR speeds catch up.

 

[oldfart]

There is already a guy running 1121 MHz FSB on an Abit 875 with an unlocked 2.8C CPU. :Q That would have required DDR560. He had to drop it down to the 3:2 for DDR375. The 5:4 would be DDR448.

 

[WizardNJ]

Hi Guys,

I'm the one with the AOPEN AX4C-Max. Looks like the Corsair XMS3200LL twin pack mem sucks on the Canterwood. Going to the dealer tomorrow to get some XMS3500C2 modules

I decided to play around and overclocked the fbs to 225 and set mem to 1.6x which equals 360 MHz.

Sandra 2003 mem scores with cpu @ 3.0 Ghz and mem @ 400 DDFR was 4636/4646. With CPU @ 3.375 GHz and mem @ 360 it is now 4915/4918. THis is with stock cpu heatsink cooling in Antec Lanboy case with extra front and rear fan.

Going to try for 250 fsb which would be 3.75 GHz with mem @ 400 DDR

I have to find a free web site to upload some screen shots.

Dave

 

[WizardNJ]

One other thing I found with the AOPEN board is when I raised the FSB to 225 MHZ the AGP/PCI divider readjusted itself to keep the AGP) at 66 and PCI at 33. Can you say cool???

Dave

 

[Jojo1971]

Corsair XMS3200LL twin pack mem sucks on the Canterwood

omg that's what i have coming for my Aopen canterwood

 

[WizardNJ]

I'm going to exchange mine for the XMS3500C2 modules tomorrow. Will post results.

Dave

 

[jhites]

Abit of overclocking
Pun intended.

 

[oldfart]

Originally posted by: WizardNJ
Hi Guys,

I'm the one with the AOPEN AX4C-Max. Looks like the Corsair XMS3200LL twin pack mem sucks on the Canterwood. Going to the dealer tomorrow to get some XMS3500C2 modules

I decided to play around and overclocked the fbs to 225 and set mem to 1.6x which equals 360 MHz.

Sandra 2003 mem scores with cpu @ 3.0 Ghz and mem @ 400 DDFR was 4636/4646. With CPU @ 3.375 GHz and mem @ 360 it is now 4915/4918. THis is with stock cpu heatsink cooling in Antec Lanboy case with extra front and rear fan.

Going to try for 250 fsb which would be 3.75 GHz with mem @ 400 DDR

I have to find a free web site to upload some screen shots.

Dave

Thanks Dave. The Sandra mem scores are kind of odd. I dont really put much stock in Sandra anyway. Some benches of actual applications would be nice if you could do them.

 

[THUGSROOK]

Corsair XMS3200LL twin pack mem sucks on the Canterwood

thats strange concidering those sticks rock on granite bay (just as good as my XMS3000 on 2.5v)

:Q

 

[Duvie]

Originally posted by: oldfart
Totally disagree. Look at how little performance increase we got when going to DC DDR over SC DDR with a ratio. Most apps 3 - 5 %. Whoopie.

Lets look at raw numbers here just using a stock 533 MHz FSB as an example. The numbers scale up as well.

533 MHz FSB DC DDR @ 1:1 = 4.2 GB/sec BW
533 MHz FSB SC DDR @ 3:4 ratio = 2.8 GB/sec BW
533 MHz FSB DC DDR @ underclocked .8 ratio. = 3.36 GB/sec BW

The 4.2 and 2.8 mem BW generally perform within 5% of each other. 3.36 GB/Sec would be even less noticeable. Here is the benefit.

An example:
Overclock a P4 3.0 800 MHz FSB CPU to 1 GHz FSB.

With a 1:1 ratio, you would need DDR that could run 500 MHz. No way. Use the 5:4 ratio, DDR400. How about performance? Lets say we used a P4 3.0 800 Mhz FSB. I'm going to say you had really good DDR that could do DDR450.

DC DDR @ 1:1
15 x 225 = 3.375 GHz
DDR450

DC DDR @ 5:4
15 x 250 = 3.75 GHz
DDR400

Which setup is faster? The 3.75 GHz by a mile.

These numbers are examples, but they work. You NEED the mem ratios is you are to do any FSB overclocking on 800 MHz CPUs. Without them, you are limited to ~ a 50 MHz FSB speed increase assuming DDR450 ram quality. That is a pathetic 12.5 % increase in FSB speed.

I totally agree...i think thugs is right to a point, but with extreme cpu speed increase the 3-5% goes out the door and many programs as you can see in the reviews still like the raw cpu speed and get no real benefot from memory bandwidth increase alone....However cpu speed increases ramp % increases well by themselves...

 

[oldfart]

Yup. And the only way you are going to get the CPU speed up on an 800 MHz P4 is to use a mem ratio. Yeah, its a bit of a compromise, but the gain in CPU MHz will way offset the very small loss in memory BW. This will the case with these setups until some much better ram comes along.

 

[THUGSROOK]

do you have any idea how hot a 3.75ghz cpu will be?
the overclocking will be restricted to cpu and fsb overclocking and hopefully you can overclock far enough to get back to 400ddr speed.

its going to be tricky, and expensive :Q
im gonna sit back and watch this time

 

[Duvie]

Thuigs is right 1:1 ratio would be the best but if the differenmce is only getting 25-33mhz fsb increase out of a chip for a few 100mhz increase in cpu speed or lower mem ratios for 800-1000mhz increase...well that is a no-brainer!!! Yes 1:1 at that speed would be much better but the fact that current ram wont do that now and thus just limit a person...

 

[WizardNJ]

Update on my memory issues with the twin pack of XMS3200LL in Dual channel DDR setup. With mem set to "by SPD" the machine would get corrupted cmos memory on reboot with mem voltage @ 2,7 volts. Wouldn't even post at 2.5 volts (this is with mem @ 400 MHz dual channel).

As PrometheusN pointed me to an article which suggested setting the memory to manual and then setting the timing to 2,2,2,6. Well that did it. Now can reboot without any cmos corruption. Sandra mem scores even went up 30 points!

I'm a happy camper!

Dave