Can a P4 with HTT obtain the full 800 mhz FSB? (long)

[Kremerica]

I have asked a lot of people and people either don't know or just don't know what they are talking about. lol
I haven't got a straight answer from anyone I asked as of yet. everyone says "well maybe"

Here is the simple question, (question is easy, the thinking gets hard)
can a Pentium 4 motherboard that supports Hyper Threading, Dual channel DDR 400 ( 4 slots, supports 2 gigs total ram) and 800mhz Front Side Bus along with a Pentium 4 chip adequate for the motherboard (say a 3.0ghz chip w/HTT) run at the full 800mhz front side bus speeds.

As I understand, when the P4 motherboards have an 800mhz FSB it is a quad pumped 200mhz bus.
so you have 4 200 mhz channels for the FSB (am I talking like your a 6 year old, and you don't know anything? yes)
so, on the motherboard it has support for dual channel 400mhz DDR memory.

The response I get from most people is that since the memory is DDR400 or 400mhz you can really only use 400mhz of that 800mhz fsb, but I don't think that is the case. Also, people tell me that to attain the full bus speeds you have to use 800mhz memory, which right now is only rdram, but I don't think this would help either b/c of the quad 200mhz bus setup.

I think, in standard operation with one memory chip (say 512MB DDR 400) you are only using 400mhz of the fsb because the memory can only talk to the cpu at 400 mhz ( "talk" = very simplified so I can understand what's going on)
but, with the dual channel you can run 2 chips (say 2x512 DDR400) which basically allows more communication sending and receiving data at the same time. so with dual channel enabled, I have been told the memory bus speeds are actually divided because the memory is talking to two processors(one physical, one due to HTT) so with dual channel setup and 2 DDR400 memory chips you are still only running at 400mhz.

Taking it one step further, if you run dual - dual channel, that's 4 memory chips (say 4x512MB DDR400) each chip is running at 200mhz which in theory uses the full 800mhz (200mhz x 4 = 800mhz). 400mhz reading and 400mhz writing,

Does this sound right ? it is just my theory after all.

Lastly, I want to make a disclaimer for myself so I don't get flamed, I don't know for sure what I am talking about, that's why I am posing the question to other, I have searched around but haven't read anywhere that it actually says the answer to my question. I have read places that say the 800mhz is overpowered for the boards, but it doesn't actually answer the question.

thanks for reading my long ass post, and thanks for any info on the subject.

 

[John]

The answer is yes. Intel quad pumps the bus. Even with a single stick of PC3200 (DDR400) you utilize the 800MHz FSB. Running 2 sticks of memory is merely a performance boost.

 

[AndyHui]

It is adequate.

PC3200 DDR RAM running in dual channel provides the full 800MHz bandwidth to RAM between the North Bridge and 800MHz FSB to the processor.

 

[JBT]

what those guys said

 

[Kremerica]

so in theory,
having 4x256MB DDR400 chips in dual dual channel would be faster than having 2x512MB DDR400 ?

is this a correct assumption ? both are 1 gig of ram, but the 4 chips of 256MB would be more efficient

 

[John]

Originally posted by: Kremerica
so in theory,
having 4x256MB DDR400 chips in dual dual channel would be faster than having 2x512MB DDR400 ?

Not unless the 256MB modules have lower cas latencies. All you need is 2 sticks of memory to achieve 6.4GB/s (full bandwidth) from the memory to the cpu.

Check the image

 

[Kremerica]

so how did you guys learn of this?
obviously it took some research, but do you read about it from intels website or is there a place where things like this get published to read about ?
thanks, just trying to get more info on it and solid evidence
not that I doubt you guys, but I have to prove it to others who I have talked to about it.

 

[MDE]

It's pretty much just multiplying the numbers.

 

[John]

All of the information, including the image I linked you to, is available on Intel's website.

You can start your research here

 

[Mingon]

I have always wondered how the motherboard transfer is synced, I would guess there is either buffers, or one bank is transfered during the first half clock cycle then the other after that.