DDR2 800, with a 1066 FSB CPU??

Hey folks.

I've been spec'ing a new PC for the new year, but it struck me last night that there may be no point in me buying DDR2 800 (PC6400) RAM for my E6600 CPU?

Surely, since the E6600 has an FSB of 266mhz (x4), any RAM I buy for it will only operate at DDR533mhz? Wouldnt I need an FSB of 400mhz for it to work at DDR2 800?

Could anyone clear this up for me please? If Im right, why do I see so many people buying DDR2 800 for C2D PC's? Is it because it will operate perfectly while increasing the FSB during overclocking?

Any help appreciated.

Here's the setup Im currently thinking of buying, encase it's needed:
-ASUS P5W DH Deluxe SKT 775
-Core 2 Duo E6600 2.4ghz
-Corsair TWIN2X2048-6400C4D DOMINATOR
-Corsair HX620 Series Modular PSU

Thanks!

all this quad pumping and crap makes things confusion I know.
But the E6600 is basicly 133mhz, and DDR2 800 is rated to run at 200mhz
Does that make sense?

ajrettke said:

all this quad pumping and crap makes things confusion I know.
But the E6600 is basicly 133mhz, and DDR2 800 is rated to run at 200mhz
Does that make sense?

Click to expand...

wrong the e6600 is 266fsb... ddr2 runs at 400 fsb x 2 (DUAL data rate so 800...)

at stock to run a e6600 @ 266fsb (266x9 = 2.4ghz) and your ram at 800mhz you need to run a 2:3 divider. 266 x 3 = 798 / 2 = ~ 400.... 400x2 = 800mhz fsb.

Ah, a 2:3 divider! Never thought of that. Makes sense now

Thank you very much for the help.

Yes, higher memory speeds make a difference. And no, if you buy 800mhz memory it wont run at 533mhz.

If you buy 1066 memory, you will have the fastest memory, even though the timmings are slower. The question is how much faster, and the answer is... Not much...

With that said, I run my board at 11x320 with a overall memory speed of 1066 (I think its a 3.33 multiplier).

Thats a nice overclock, with great memory speeds and really low temps.

Mike

Now im really friggin confused

If this dude gets his (PC6400) RAM + E6600 CPU, can he still have 1:1 FSBRAM ratios?

at attainable clocks on air cooling.. DDR2-800 + E6600 = 3.6Ghz. for 1:1 ram ratio.

but most decent ram can overclock to at least 400FSB so its not that big a deal when using a CPU with a 9 multi. Its when the multi's get lower that things get more complex (ram and motherboard selection)

800 mhz isnt 1:1

1:1 is 266
2:1 is 532
3:1 is 798 (wich is actually 800 mhz due to rounding problems associated with the orriginal memory spead)

The 1066 is a constant speed based on a FSB x 4. This seems to be the speed the CPU comunicates to the FSB and not the memory itself. The Memory is held back by a "Multiplier" and the default non-overclocked speed for Dual 2 Core processors is 800mhz. Anything above 800mhz is considered an overclock by both the Motherboard Manufacturers and the Corsair company.

This makes things tough for people who want to push the Memory over 800 on some motherboards. My Gigabyte DS3 couldnt handle 1066 memory (4:1), it started to fail around 950mhz. My Gigabyte DQ6 does 1066mhz even on processor overclocks (thus using lower memory multipliers as I stated above).

some people claim 1:1 is 532, however this seems to be incorrect to all references outside a few members of Tomshardware that soon left after these statements (they left cause tomshardware is full of flamers and lamers).

Now the real fun starts... As you increase your FSB you start increasing that 266x4 speed which is the one that communicates with the North Bridge. As you increase these speeds the chip or the Northbridge can start failing. Thus your FSB even if your running a memory multiplier lower then your memory rated speend.

Mike

Can someone provide a no-nonsense senerio for an e6300, e6400, and e6600 running 1:1 ratio with memory rated at PC2-6400. I am not absorbing this information very well

No-Nonsense for DDR2??? Impossible...
I am unclear of what info you want me to provide.

GJ/Mike.. DDR2-800 the number 800 is double pumped (being DDR2).. so the FSB mhz is 400... the mulitplier on the E6600 is 9 that would pretty much top out the chip on high end air cooling, 400 X 9 = 3600mhz or 3.6Ghz.
Thats if the ram isn't overclocked

Thats assuming you want to use a 2:1 memory multiplier. I generally like higher memory multipliers with lower FSB... I dont see any difference in the overclocks when I drop it down to a 2:1 memory multiplier and pump up the FSB... Infact, I get less reliabilty.

I think sniper needs to understand this
4xFSB = Northbridge Communication Speed
Memory Multiplier x FSB = Memory Speed

The highest Memory Multiplier you can have is 4...

I run a 4 at 266 and I get 1067 (the speed of my memory)
I am running 320 at 3.3333 and I get 1066 (Again the speed of my memory)

320 (FSB) x 11 (cpu Multiplier) = 3.52ghz (my clcok speed)

Its reliable and runs really cool... water always runs bellow 90f though today after some NFS Carbon I hit 91f.

The higher the FSB the hotter the Northbridge should get, and the NB Part of the CPU should get pushed harder. NOTE: This is an assumption I have that is based on loose observations

Mike

no.. stock frequency is 400FSB on DDR2-800 with the 1:1 ram ratio.

LOL. I think everyone here that is trying to understand how memory works, is now worse off for have reading threw this thread LOL, J/K. I've been around this stuff for awhile now and even I got confused reading threw this.

Keep it simple. First of all forget about all your RAM dividers. All the original poster wants to know is if he really needs DDR 800 in order to overclock his e6600. Like greenmaji was saying, the e6600 has a muliplier of 9, and the most you can hope from a good e6600 on air is around 3.6Ghz. So we pop open our calculators and do a trusty equations: (CPU Mhz) / (CPU muliplier) = (FSB). so we go 3600/9 = 400(<- thats 400mhz fsb). If memory is running 1:1 then FSB mhz and memory mhz are the same. So, if your e6600 overclocks to 3600mhz then your memory would be running at 400mhz DDR800 speeds(400mhz memory on dual channel = DDR 800).

I think some memory that is good to at least DDR800 speeds is a good idea if you plan to overclock a C2D. In the end you just have to decide how far you want your cpu to be able to overclock. Say you go cheap and get some memory thats only good for DDR667 speeds. DDR667 would be running at 333mhz. So 333mhz times a multiplier of 9 = a max overclock of 2997mhz. Not enough if you ask me.

hyperasus is trying to keep it as simple as possible, he's refering to stock ram speeds.. not overclocked
thats when things get a little more complicated.

The problem is that each motherboard manufacturer labels the multiplier differently.

Asus and Wusy (who use to be at Toms Hardware, but left cause Toms Hardware sucks), claims 1:1 was 533. Gigabyte counts a memory multiplier 2:1 with a stock fsb as having 533mhz CPU speed.

STOCK speeds are 800mhz regardless of what the multiplier is, with a FSB of 266 (which Gigabyte lists as a 3.0 multiplier). 266x3=798 (with some weird rounding).

I think default FSB is 266.666....

Default DDR is 400mhz, however eventually they started to use it in parrel... so it was 800mhz with 2 chips.

DDR2 is 800mhz, and actually HAD slower timings at first then DDR.

DDR2 is a nightmare when it comes to the compatability issues motherboards are having with it.

Mike

Gigabyte is the only company that has a strange "multiplier" situtation that I know of.. they dont use a ratio but a number to mulitply the front side bus with.. so..

Other motherboards ram ratio of 1:1 on Gigagabyte boards is (front side bus) X 2 in the bios. Front side bus is understood.

Reading the manual reveals this information however
So, Green Jelly could you read the ram configuration section of your manual and get back to us on the difference between the Frequency of DDR2 (in our example DDR2-800) and the effective front side bus Mhz (400mhzFSB), thanks.

ajrettke said:

all this quad pumping and crap makes things confusion I know.
But the E6600 is basicly 133mhz, and DDR2 800 is rated to run at 200mhz
Does that make sense?

Click to expand...

this is the most no-nonsense explination ^^^

CPU FSB = 266mhz
DDR2FSB = 400mhz

DDR2800 has a faster FSB and will be fast enough if you want to overclock - you will not hit a memory bottleneck until your CPU FSB hit 400Mhz.

greenmaji said:

So, Green Jelly could you read the ram configuration section of your manual and get back to us on the difference between the Frequency of DDR2 (in our example DDR2-800) and the effective front side bus Mhz (400mhzFSB), thanks.

Click to expand...

Why the attitude? If I made a mistake, please just say that I made a mistake, what that mistake was, and where you found out that I made a mistake. I am human, and I do make mistakes...

I also can only read the same motherboard manual so many times before I loose my mind and shoot someone Its like a meter in my head... Every time I open the book, the number clicks, and its one less then it was a moment ago... eventually, and this hasnt happened yet, the number hits 0... and at that time, aliens take over my brain and I go on a mission to clense the earth of humanity so that they may come down and live happily, with a clean environment, polution free cars, amazing sounding speakers, 8mm ID Water cooling systems, and computers that run so fast you dont even know there on.

The problem is that the true memory multiplier has a true answer out there... yet no one seems to know the real answer I certainly dont, for it seems to depend on the forum you goto and who your talking too.

People on Tomshardware claim 1:1 is 533 mhz (266 fsb)... If you say its anything else you will get flamed. Its crazy, but I dont try to change it... I just go with the common language people use.

I personally like Gigabytes approach. Give me a number to multiply my FSB to find out the resulting MHz my memory will run at. I find it Simple... Ratios are a bit to much math for me sometimes.

But thats my opinion...

Klutch said:

Here's the setup Im currently thinking of buying, encase it's needed:
-ASUS P5W DH Deluxe SKT 775
-Core 2 Duo E6600 2.4ghz
-Corsair TWIN2X2048-6400C4D DOMINATOR
-Corsair HX620 Series Modular PSU

Thanks!

Click to expand...

Klutch, using the info above if you want to run the memory at the same speed as your CPU's stock speed, the memory will run at a 1:1 ratio which will equal FSB266mhz/DDR2 speed 533mhz. PC6400 aka DDR800 memory can be downclocked to DDR533 speed.

If you want to run the stock speed of the memory you will need to OC and increase your CPU FSB to 400mhz and memory will be at 400mhz. However, there is no guarantee your CPU can do this.

So, do you plan to OC or not?

To keep it simple, DDR (DDR1 or DDR2) stands for dual data rate memory meaning that it transfers data 2 times per clock cycle. So, DDR533 memory is actually running at 266mhz (266.66> actually) but the effective data rate is 533mhz. So, DDR533 is at a 1:1 ratio with a 1066 FSB CPU at stock speed.

Intel CPUs have 4 pipelines that communicate with the memory controller on the MOBO. Each individual pipeline is running at 266mhz at stock speed. So, the effective rate here is 266mhz x 4 pipelines = 1066mhz FSB.