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1333 FSB Confusion.

SH4RKY

SH4RKY

SH4RKY

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If the CPU and mobo both can support a FSB of 1333mhz. Why is 800mhz ram usually recommended??

Surely DDR3 ram that supports 1333 is a better choice?


Or have I missed the point somewhere??




(hmm… maybe its 800mhz ram that’s suggested for the 1066FSB CPUs.)


Ulgh, confused. Anyone care to explain things for me? :)
 
1333mhz FSB is quad pumped meaning that it is actually 333mhz (ish) DDR2 runs @ FSB *2 so at 333mhz the RAM runs at a frequency of 666mhz.. within its 800mhz max supported Frequency

so for instance to run 800mhz RAM higher than its "design spec" you would have to run a FSB of above 400mhz (1600mhz quad pumped)
 
I think i get that. If i was asked to expalin that to someone else then i probably couldnt though... haha


So 800mhz (ddr2 6400) ram is still more than enough even for the worfdale cpus? and considering most ram can be overclocked to the next band there is room for movement if the Mobo supports up to 1600 fsb.
 
So 800mhz (ddr2 6400) ram is still more than enough even for the worfdale cpus? and considering most ram can be overclocked to the next band there is room for movement if the Mobo supports up to 1600 fsb.
Click to expand...
It depends.

If you want to keep the RAM running within stock ratings, then with a 9x multi (E8400) and PC2-6400 you can get 3600 Mhz (400 x 9) but with PC2-8500 you could get 4797 Mhz (533 x 9). How high do you want to go, that is the question?
 
SH4RKY said:
Ulgh, confused. Anyone care to explain things for me? :)
Click to expand...
I think Pneumonic covered it but I will cover it in more detail! :cool:

Many years ago it was a lot simpler, there was just an FSB speed and a memory speed and there were both the same, for this example lets say it was just 100MHz

Front Side Bus= 100MHz
Memory Speed= 100MHz

All very easy so far . . . but then there was a change and I think it was AMD who bought it first to the mainstream and it was a double-pumped FSB which technically is called a System-Bus

Front Side Bus= 100MHz
System Bus (Double Pumped FSB)=200MHz
Memory Speed= 100MHz

All this changed meant was that any information passed between the CPU and the memory (+ other bits of the chipset) had its speed doubled therefore helping to remove the FSB from the overall speed bottleneck.

I think then AMD upped the speed of the FSB system BUS which of course required faster memory also to keep up . . .

Front Side Bus= 133MHz
System Bus (Double Pumped FSB)=266MHz
Memory Speed= 133MHz

At this point every computer enthusiast/gamer were loving up AMD big time and INTEL wasn't so happy about this so the Blue Giant revised its chipset to not only support a faster FSB speed but also a quad pumped System-BUS. . .

Front Side Bus= 133MHz
System Bus (Quad Pumped FSB)=533MHz
Memory Speed= 133MHz

Soon came along DDR with its Double Data Rate (x2) to try and help keep up with the now uBer System-Bus

Front Side Bus= 133MHz
System Bus (Quad Pumped FSB)=533MHz
Memory Speed= 133MHz
Effective Memory Speed= 266MHz

And it wasn't long before the FSB was hiked from 133MHz to 200MHz

Front Side Bus= 200MHz
System Bus (Quad Pumped FSB)=800MHz
Memory Speed= 200MHz
Effective Memory Speed= 400MHz

I think if you have read through the above it should become quite clear how things link up, I just felt it was worth making the difference between FSB and System BUS (or rated FSB) clear!

It is a bit confusing at first so helpfully this post helps! :)
 
great explanation!

Think undestanding FSB and memory is one of those things that seem confusing as hell to begin with, and as soon as you understand it seems so obvious!
 
:) Thanks for the explanation.

I think it would become even clearer if I had a system to play with and see the real world numbers altering infront of me.


So with a Q6600, some DDR2 6400 ram and a PQ5 mobo, what would the stock numbers be in terms of Front Side Bus, System Bus (Quad Pumped FSB), Memory Speed, and Effective Memory Speed??

I'm guessing
Front Side Bus= 266MHz
System Bus (Quad Pumped FSB)=1066MHz
Memory Speed= 400MHz
Effective Memory Speed= 800MHz


So where does CPU clock speed come into these numbers?
 
Great post Big.Wayne, I thought I had a pretty good understanding - but you've certainly filled in some gaps to help clarify a few things for me *BIG thumbs up* :D
 
Ok, so a q6600 at stock would be:
FSB 266 x 9 multiplyer = 2.4ghz.

So overclocked to 3.0ghz and the ram at 8500 speeds it would something like this:

Front Side Bus= 333MHz
System Bus (Quad Pumped FSB)=1333MHz
CPU = 333x9 = 3ghz

So can ram be separated from the CPU clock?
Memory Speed= 533MHz
Effective Memory Speed= 1066MHz
But timings would take a big hit to achieve that. Whats better, faster mem speed or faster timings?
 
So overclocked to 3.0ghz and the ram at 8500 speeds it would something like this:

Front Side Bus= 333MHz
System Bus (Quad Pumped FSB)=1333MHz
CPU = 333x9 = 3ghz
Click to expand...
No, PC2-8500 runs at 533 Mhz.

FSB = 533.
CPU = 533 x 9 = 4797 Mhz.

So can ram be separated from the CPU clock?
Click to expand...
RAM is seperate from the cpu clock, it is dependent on the FSB.

You can have RAM running faster than or equal to the FSB but not less than.
 
Ok.

I've noticed PaulDs numbers in his sig. Q6600 @ 3.6Ghz (8x450) 4Gb Crucial ballistix @ 1080Mhz 5-5-5-15. So His overclock numbers would look like this:


Front Side Bus= 450MHz
System Bus (Quad Pumped FSB)= 1800MHz ? isnt the boards max FSB 1600?
Memory Speed= 540MHz
Effective Memory Speed= 1080MHz
Cpu Clock 450 x 8 = 3.6ghz
 
Officially 1600 FSB is the max for even Intel X48 boards but officially your CPU is 2.4 Ghz, so... :p

I'm guessing he is using 4:5 divider with the FSB:RAM but you'd have to ask him!

450 x 8 achieves the same as 400 x 9 but the latter doesn't overclock PC2-6400.
 
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