OCing and Memory

[fuzzy34]

Ok, so I am pretty confident on the following parts:

C2D E6750 2.66Ghz (1333 FSB)
Asus P5K-VM or Gigabyte GA-G33M-DS2R
Unknown brand memory DDR2 - 800 or 1066

Now here's my problem. I am unsure as what speed memory I actually need to purchase. The motherboard specs show DDR2-1066 as the memory standard, but 1333/4 = 333 which means I should only need DDR2-667 memory.

Also, I plan on doing a small overclock (up to 3.0 Ghz). I already know I probably won't be able to simply use the multiplier, so upping the FSB will be required. A bus speed of 375 will give a CPU freq of 3.0 (375x8), but 375*4 = 1500 FSB after its quad-pumped. Am I right in this way of thinking on the quad-pumped FSB? Does it need to be 1333 like the proc was rated at?

All help is appreciated!

 

[BillParrish]

Forget the quad pumped number after you have divided it by 4 to get the "true" FSB.

You math is correct, everything you said was correct. but the cpu number that matters is its actual running speed which is the cpu mulit x the "true" FSB.

The "Buss Speed" advertised by Intel is PR "non-information". Intel chips can perform up to 4 operations per clock cycle so to make them sound faster they just started naming them with the pseudo-Buss Speed, marketing mainly but I guess some credit goes to enginnering on making the cpu more efficient.

See my sig my 800MHz Buss Intel CPU is running at an 470 x 4 = 1880 "Intel rated" bus and is very happy.
Your memory speed will run at 2 x the "true" FSB.



Here is my standard blurb on Core 2's vs Memory speed and how to select the one right for you.

PC6400 is probally fine for any C2D quad or otherwise based on the following:

Using a CPU mulitplier of 8 (all c2d have this multi except the E6300 and one other I cant think of, the cheapies, check your cpu)

Using an FSB setting of 400MHz (all good enthusiasts OCing boards should be able to do that)

Setting the memory mulitplier to a 1:1 ratio (the memory runs at twice the speed of the FSB, which is the way Intel designed the chipset, other ratios are available but in general you want to run at 1:1)

if you do the above your CPU is running at a very respectable OC of 8x400 = 3.2GHz and your memory is running 2 x 400 = 800 MHZ right on spec and not overclocked at all. This leaves you room to increase the FSB some more. Most decent OCing memory will get to 430MHz FSB (860MHz memory speed) before you need to loosen the timings to go higher, see my sig. So typically you should be able to get somewhere near 430x8 = 3.44GHz. Of course top notch cooling and proper setup etc etc.


Some C2Ds have multi of 9 which allows a lower FSB to reach the same CPU frequencies but you end up under clocking your ram. for example, 9 x 357FSB = 3.2GHz CPU speed but your memory is only running at 2x357 = 714MHz which is under its rated speed and you loose memory bandwidth. If next available memory mulitplier/divider (check each proposed board for the exact memory dividers it supports,) was 2.5 and you enabled it your CPU would still be at 3.2 but your memory would run at 2.5 x 357 = 892MHz which might be high on fast timings and require you to loosen timings up just to boot. In this case ram rated higher than PC6400 would be preferred.

So it just depends on how hard you are going to push it, good very respectable OC without stressing stuff pc6400 will do very well. You want to push as hard as you can get something rated a bit higher. 4GB (4x1GB typically reduces the ability to overclock just a tad)

Thats the facts. Download the manual for the board you are considereing and do the easy math based on available memory dividers and see what you can do (in theory).

 

[fuzzy34]

Thanks for the thorough reply! I was pretty sure that the DDR2-800 (400 FSB) memory would be fine given my math and that I only needed to run at 375 FSB, which of course is still slower than the rated speed for DDR2-800 memory (yay to trying to tighten up the timings!).

Also, so the memory standard given by the motherboard specs is simply the maximum speed supported by the motherboard, right (not a requirement for the board)?