800 Mhz Frontside bus?
 

Hi there, do you actually get 800 MHz on the front side bus or are you limited
by the memory clock speed, i.e. DDR 400? Or is the 800 MHz only between the processor
and the controllers (memory, north and south bridge)?

Matt

"Matias" wrote in message
...

Hi there, do you actually get 800 MHz on the front side bus or are you
limited
by the memory clock speed, i.e. DDR 400? Or is the 800 MHz only between
the processor
and the controllers (memory, north and south bridge)?

Some chipsets can run the CPU FSB at a different speed from the memory
bus. This is often a big win if you have a chipset where the graphics memory
is also main memory.

DS

In article , David Schwartz wrote:

"Matias" wrote in message
...

Hi there, do you actually get 800 MHz on the front side bus or are you
limited
by the memory clock speed, i.e. DDR 400? Or is the 800 MHz only between
the processor
and the controllers (memory, north and south bridge)?

Some chipsets can run the CPU FSB at a different speed from the memory
bus. This is often a big win if you have a chipset where the graphics memory
is also main memory.

You also have to keep in mind that both that 800MHz and the 400MHz are
somewhat misnomers. Both busses physically run at 200MHz. It's just
that the bus to the CPU is "quad pumped"--that is it transmits 4 times
per clock tick--and the memory bus is "double pumped". So, yes, they
can run at their "different speeds" at the same time, becuase they're
actually the same speed.

--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University

System FSB is 200 MHz.
Double data rate (DDR) RAM runs at double the system's FSB, thus at 400MHz.
The CPU runs Internally at four times the system's FSB, thus = 800 MHz.

--
DaveW



"Matias" wrote in message
...
Hi there, do you actually get 800 MHz on the front side bus or are you
limited
by the memory clock speed, i.e. DDR 400? Or is the 800 MHz only between
the processor
and the controllers (memory, north and south bridge)?

Matt

But what good is the 800 MHz FSB when the memory is only good for 400 MHz
isn't the true speed the lowest common denominator

Nate Edel wrote:

Matias wrote:

Hi there, do you actually get 800 MHz on the front side bus or are you limited
by the memory clock speed, i.e. DDR 400?


Actually, you get 200mhz on the front side bus... the P4 bus is QDR
("quad-pumped") so you get an effective 800mhz transaction rate on a 200mhz
clock.

That said, you only get the full 6.4gbytes/sec (800mhz * 8 bytes on a
64-bit-wide bus) if you have a dual channel memory system...

On Fri, 07 May 2004 10:23:22 -0700, Matias Silva wrote:

Nate Edel wrote:

Matias wrote:

Hi there, do you actually get 800 MHz on the front side bus or are you limited
by the memory clock speed, i.e. DDR 400?


Actually, you get 200mhz on the front side bus... the P4 bus is QDR
("quad-pumped") so you get an effective 800mhz transaction rate on a 200mhz
clock.

That said, you only get the full 6.4gbytes/sec (800mhz * 8 bytes on a
64-bit-wide bus) if you have a dual channel memory system...


But what good is the 800 MHz FSB when the memory is only good for 400 MHz
isn't the true speed the lowest common denominator

Do the math: with a dual-channel DDR400 memory implementation and a dimm on
each channel, the peak memory bandwidth matches the
800 Mega-transfers-per-second FSB....

/daytripper