FSB question

[vanhalen]

Hello there,
I am trying to figure out somthing for quite some time.

if I got a conroe with support of 1066MHZ FSB
and I got a mobo with the same support.
but I got DDR2 with only 667MHZ.

and everyone says that without OC I dont need faster RAM.

so what am I missing here?

Thanks

 

[1Tanker]

Hello there,
I am trying to figure out somthing for quite some time.

if I got a conroe with support of 1066MHZ FSB
and I got a mobo with the same support.
but I got DDR2 with only 667MHZ.

and everyone says that without OC I dont need faster RAM.

so what am I missing here?

Thanks

Okay, Conroe uses a 266MHz FSB. That bus is quad-pumped...giving an "effective" FSB of 1066MHz. Your motherboard also supports those speeds. Now, although the processor FSB is running @266MHz, the RAM is DDR(double-data rate)meaning it transfers twice as much data per clock cycle. So, with an FSB of 266MHz, your RAM (running synchronously...1:1)is running @ 533MHz..and effective 1066FSB. Running the RAM @ the same speed as the FSB(synchronously), is the best setting with a Core2Duo processor, meaning for great performance, you only need DDR2-533. Your DDR2-667 will run @ 667MHz(333FSB) if needed, but you can still run it at 533MHz. Sorry, if that's tricky to follow, but those are the basics. GL

 

[vanhalen]

Thanks 1Tanker

but I still dont get it
DDR2-667 real freq is 333MHZ !
DDR2-533 real freq is 266MHZ !

with DDR technology, the real freq multiple by 2, so

DDR2-667 effective freq is 667MHZ !
DDR2-533 effective freq is 533MHZ !

but why do we multiple the effective freq in 2 also?

 

[vanhalen]

you have 2 channels of memory in parallel

you mean DUAL CHANNEL technology?

 

[vanhalen]

correct me if i'm wrong. but
DUAL CHANNEL means memory interface with 64bit instead of single channel which works with 32 bit.

 

[Mandrake_]

Single channel = 64bit
Dual channel = 128bit

Dual Channel 533mhz DDR2 matches a 1066mhz FSB. 667mhz DDR2 in dual channels matches up a 1333mhz FSB.

 

[vanhalen]

Single channel = 64bit
Dual channel = 128bit

sorry, my mistake.

but Dual Channel doubles the bandwidth, not the freq. :?

 

[misry]

DDR's effective clock doubling is because the ram performs operations on both the leading edge of the square wave and the trailing edge. It, effectively, does two things every time the clock ticks.

 

[jamiepotter]

Thanks 1Tanker

but I still dont get it
DDR2-667 real freq is 333MHZ !
DDR2-533 real freq is 266MHZ !

with DDR technology, the real freq multiple by 2, so

DDR2-667 effective freq is 667MHZ !
DDR2-533 effective freq is 533MHZ !

but why do we multiple the effective freq in 2 also?

I think the short answer is... we don't. Look, just work out what your external FSB is. As 1tanker said, this will be 266 on a core2duo. Now:

Your mobo's FSB will be that x4.
Your CPU's internal FSB will be that x7 (e6300) or x8 (e6400) or x9 (e6600)
Your memory will run at that x2 (on a 1:1 divider, anyway)

Don't worry too much about the 'effective' speed.

 

[vanhalen]

so what you are saying,
just as I calculate the cpu FSB (266*4=1066)
I do the same thing with the memory?
real freq *4 ?
meaning
DDR2-533 -> 266*4 = 1066
DDR2-667 -> 333*4 = 1333

is this the equation ?

 

[jamiepotter]

No. Look, your memory will still operate at your external clock or FSB (the raw number that everything else is multiplied by) x 2. Your CPU will operate at your external clock x7, or 8, or 9, or whatever it is. The total speed at which your CPU can get information from the memory is determined by your external clock x4. This is the bus between the memory and the CPU, sometimes called the MCH or the Northbridge.

You might be confused by the idea that even though memory in dual channel mode will effectively run at quadruple the speed of the external clock, it is only rated at double the speed. This is because it is only true of the memory _bus_ that it goes 4x the ext clock speed (i.e. 2 sticks of DDR2-533 memory in dual channel mode will be able to transfer the same amount of info per second as 1 stick of DDR2-1066 (if there is such a thing, which there probably isn't)), but false of the memory _modules_. The memory itself will only operate at the external clock speed x 2. It's just that a motherboard feature (dual channel mode) makes the two sticks of memory work in tandem rather than treating them as one big stick.

So the CPU getting info from the memory would look like this (assuming a 1:1 divider):

Memory stick 1 (ext clock x2) + Memory stick 2 (ext clock x2) -> Northbridge (ext clock x4) -> CPU (ext clock x9, say)

In dual channel mode, your northbridge and your memory are effectively working at the same speed (on a 1:1 divider), although one is rated FSBx2, and the other is rated FSBx4.

All you really need to know is that the way DDR memory is rated is simply by doubling the external clock, and the way the mobo's FSB is rated is simply by quadrupling it.