P5B Deluxe & Q8400: FSB Question

[menthol1979]

Hello all,

I have this rig:
M/B: ASUS P5B Deluxe (BIOS 1238)
CPU: Intel Core2 Duo E6400 (2.13 GHz, 1033 FSB)
RAM: Kingston HyperX KHX6400 4GB DDR2 PC6400 800MHz CL4
GPU: ASUS EN7600GT
HD: Seagate Barracuda 1TB 7200 SATA2

I'm running Windows 7 x64. So far, this is the best, most stable and reliable system I've ever made. However lately, especially after the 7 upgrade, I think I need some more CPU. Since unfortunately I cannot affod mobo/ram change etc, I'm thinking to change only the CPU to a Q8400 which I find in a nice price here.

My problem is that CPU's FSB is 1333. Someone told me that if I want to upgrade to this CPU, my RAM cannot sync at 800 no more, but I have to sync it lower (667 I think) so that RAM/FSB is at 1:1. Is this true? I need you help here... Now Hyperx is at 800/1.85V/CL4-4-4-12.

Thanks, Nikos.

 

[Rafael]

With the E6400 you were running memory in asynch mode, since it had 266 FSB and mem probably running @ 400 Mhz. If you were not OCing ur system.
Now with the Q8400, I think it will be the same FSB will be in 333 Mhz and the mem will be @ 400 Mhz if you leave in auto, or you can set manually the dividers in BIOS. I can't remember right now, since I had long time ago this mobo.

BTW, welcome to AT!

 

[elconejito]

Rafael is correct, I believe. You may have to set the FSB to 333 if it doesn't automatically do it, and then you may have to set the memory divider so that the RAM stays at 800mhz if it doesn't do it automatically.

The thing you will have to verify first is if that CPU will work on that board. I used to have that board (loved it), but it's compatibility with newer CPUs is spotty. Even if it's on the supported CPU list, I'd google around the mobo model and CPU model and see if others have had issues. Other than that it should be a nice upgrade for you.

 

[menthol1979]

Thanks for your replies and nice to meet you!

I am not OCing my system since E6400 was not ideal for this purpose. Not to mention that Kingston sticks are nice and stable but not good for OCing... I learnt that afterwards.

Anyway, I will still be in async mode, with whatever drawbacks this imposes, but after all, as you mention, it would be an upgrade that will last at least a year -maybe more- until I buy a new rig. The ideal would be to keep the 1:1 ratio (with 1066 sticks probably). From around the web, it seems that not many people have this CPU but all of those who have it, report stability.
So I think I'll go ahead. Thank you!

 

[Rafael]

Yeah what I meant is probably if you leave in auto, the system will detect everything fine, and it will run async the memory @ 800 Mhz just fine, and if it doesn't, it just can be adjusted manually.
Another thing to keep in mind is to update the BIOS, I do not know what version you have, but since the Q8400 is a "recent" cpu, you might update ur BIOS.
For the stability point I dont see much problem, since your system will be running @ stock.
If you run the system 1:1 you will be running your memory @ 667 Mhz, not @ 800 Mhz as your memory is rated for. But I am pretty sure you will have to set in BIOS to run the memory synced.
And either situations running async or sync, you should have a stable system @ stock.

 

[nipplefish]

I am not OCing my system since E6400 was not ideal for this purpose.

I disagree.

Run your memory 1:1 at 533, then crank up the FSB. I've got mine at 350x8 for 2.8ghz currently without modifying voltage or anything.

 

[menthol1979]

I disagree.

Run your memory 1:1 at 533, then crank up the FSB. I've got mine at 350x8 for 2.8ghz currently without modifying voltage or anything.

Maybe I'm wrong about the E6400, but surely Kingston won't handle 533. But if I sync ram to 533 and FSB to 350, I'll be out of 1:1 again, right?

 

[Rafael]

Hey menthol1979,

I think you are confused about FSB and processor bus, and I will try to explain to you, and maybe someone can explain clearer to you.
But since your system, Intel P965 and Core 2 Duo or Core 2 Quad, uses DDR2, the system will be quad pumped in the bus, to get to 1066 Mhz bus speed you only need the 266 Mhz in the FSB to achieve that bus. So FSB @ 266 = Memory @ 533 Mhz = CPU bus @ 1066 Mhz.
So setting the FSB to 533 Mhz would throw the processor bus to 2133 Mhz, and I doubt that either your processor, mobo or memory would handle that.
But since you have PC2 6400 memories (800 Mhz), that could you take to 400 Mhz and a bus of 1600 Mhz, what is quiet possible like nipplefish said.
So to run memory @ 533 Mhz it will only take 266 Mhz in the FSB.
And you will have memory dividers to run memory async, I can´t remember right now what are the dividers on top of my head, so you will run FSB @ 266 Mhz and your memory @ 800 Mhz, just an example.

Hope that helps to understand a little bit.

 

[menthol1979]

Hey menthol1979,

I think you are confused about FSB and processor bus, and I will try to explain to you, and maybe someone can explain clearer to you.
But since your system, Intel P965 and Core 2 Duo or Core 2 Quad, uses DDR2, the system will be quad pumped in the bus, to get to 1066 Mhz bus speed you only need the 266 Mhz in the FSB to achieve that bus. So FSB @ 266 = Memory @ 533 Mhz = CPU bus @ 1066 Mhz.
So setting the FSB to 533 Mhz would throw the processor bus to 2133 Mhz, and I doubt that either your processor, mobo or memory would handle that.
But since you have PC2 6400 memories (800 Mhz), that could you take to 400 Mhz and a bus of 1600 Mhz, what is quiet possible like nipplefish said.
So to run memory @ 533 Mhz it will only take 266 Mhz in the FSB.
And you will have memory dividers to run memory async, I can´t remember right now what are the dividers on top of my head, so you will run FSB @ 266 Mhz and your memory @ 800 Mhz, just an example.

Hope that helps to understand a little bit.

Thanks Rafael! What I was confused about is that MEM FSB is multiplied by 2 (that explains 400x2=800) and CPU is FSBx4, that is 266 x 4 = 1066. If I got it right this way.

Now Q8400 will use 333x4 = 1333 FSB, and I have two options: Either run asynchronusly, that is mem @ 400 & cpufsb @ 333 ... or, why not, try to OC the Q8400 a little to 400x4 = 1600 FSB. I'll give it a try!

 

[Rafael]

Exactly menthol1979!!!

That is it! You got it perfect!
Just a heads up if you are going to OC, I do not think it is going to be hard, but it will take a little time and some tries.
But usually to OC to 400 Mhz FSB, you will run vcore, vdimm, @ default settings, the only thing is to set those settings manually in the BIOS, because if you leave in auto, the system will up the voltages, etc to keep the system stable since you raised the FSB.
But I think it will not be necessary.
I will take my system as example: my CPU is E6400 conroe with default vcore up to 1.35v, if I OC and leave system in AUTO, the system will raise my vcore to 1.325. But to run OC my CPU gets stable with 1.2785v, so I set all manually.
It will only take sometime, but you can always ask for help and directions here @ AT!
Besides the P5B does not have the same amount of parameters like the new mobos.

Regards!

 

[menthol1979]

Thanks Rafael! I am quite familiar with OCing, had a Celeron 700 @ 890 veeery long ago and I can put my hands back on this stuff vdimm is already touched (2,1 to run on 800 otherwise stays 667). Well, trial and error applies here also!

Million thanks for your support, and to all of you

 

[OptotsshorP]

I used that mobo with more than 500FSB with PL 6 or 7...The only problem I had with this mobo was its "death". One resistance near the cpu socket jumped off and I dunno how/why..But it was the best mobo Ive tested