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Confused on calculating overclocking

B

budman76

n00b
Joined
Mar 9, 2008
Messages
32
Its been a while since I've overcloked my P4 chip, and after reading Graysky's excellent guide I'm still confused.
My P4 chip is 3.0Ghz with and multiplier of 15 and FSB of 200 thus 15X200=3.0 GHZ
so when I increased my fsb to 217, I was overclocking at 217X15=3.25 Ghz. Therefore I needed memory that would support a speed of 217 x 2=434 (I have DDR2 433)
My question is with dual core chips like E8400 the formula is 333 X 9 (multiplier)=3.00Ghz
Where did the 333 fsb come from? (I thought the FSB was 1333?) and what about quads? I need to understand this relationship so that I can get the correct speed RAM. I hope I'm making sense.
 
The 1333MHz FSB figure is quad-pumped, so the true FSB is 1333/4 = 333MHz (give or take a quarter of a megahertz). It's the same idea for quad-cores, their FSB is quad-pumped as well, so a Q6600 with a stock FSB of 1066MHz has a real FSB of 1066/4 = 266MHz - for the Q6600, 266*9 = 2.4GHz.
 
Then take the 1333/4 number of 333mhz FSB and multiply it by 2 to get your DDR speed at 1:1 ratio. You can also run a 5:4 ratio or 3:2 depending on the board you're looking at.

Pretty much any DDR2 800 memory will work fine because most boards will run 1:1 and 400mhz is usually good enough of an FSB. The only time you might need more is if your CPU has a low multiplier and you need a high FSB to reach the max of your CPU. If you need 500mhz FSB, you might need DDR2 1000 memory.

DDR2 800 memory with Cas 4 timings will usually loosen up and OC past DDR2 800 speeds at Cas 5 timings with a little extra voltage.
 
Thanks Mithent & Kirbyrj, I didnt realize the both the Dual core AND quad core had their FSB quad pumped and both needed to be divided by 4.
 
budman76 said:
Thanks Mithent & Kirbyrj, I didnt realize the both the Dual core AND quad core had their FSB quad pumped and both needed to be divided by 4.
So I just need to divide the FSB by four and then multiply by 2 to figure the DDR ram speed needed then, example 1333Mhz FSB/4=333Mhz X 2 = DDR2 666?
Click to expand...

Yes, if you're running 1:1 ratio. If you're running 5:4, you take 333/4 then multiply x5 to get the memory speed you want.
 
I'm not sure if it's more or less stable, but the real advantage of running the ratio is allowing your memory to run at higher speeds which would mean more memory bandwidth (and higher synthetic benchmark scores). Real world, I'm not sure you'd notice the difference between 1:1 and 5:4 or 3:2.

Where you would notice it is in OCing where your memory is the "weak link." 1:1 is usually the lowest allowed multi, thus you'd set it at that to max out your OC while running "cheap" memory. DDR2 1000 memory is usually twice as much, and you theoretically wouldn't need it.
 
your ratio

then your FSB speed x your multipier.

ex. i am running 1:1 ratio 425mhz FSB x 8.0 = 3400mhz clock speed
 
powderkid said:
your ratio

then your FSB speed x your multipier.

ex. i am running 1:1 ratio 425mhz FSB x 8.0 = 3400mhz clock speed
Click to expand...

I have my wife's computer as well as my son's computer both running an overclocked E6420 processor. Factory is 2.13ghz. They are overclocked to 3.4ghz (425 FSB x 8 multiplier), running DDR2-800 memory at a 1:1 ratio.

To the Original Poster: what motherboard do you have and what kind of ram are you using or would like to use?
 
officermartinez said:
I have my wife's computer as well as my son's computer both running an overclocked E6420 processor. Factory is 2.13ghz. They are overclocked to 3.4ghz (425 FSB x 8 multiplier), running DDR2-800 memory at a 1:1 ratio.
QUOTE]

if your running 425FSB then wouldnt you need DDR2-850 (DDR-1066 since there is no DDR-850) to keep a 1:1 ratio?
Click to expand...
 
budman76 said:
if your running 425FSB then wouldnt you need DDR2-850 (DDR-1066 since there is no DDR-850) to keep a 1:1 ratio?
Click to expand...


Well "over-stepping" the advertised ratings of your memory is basically just overclocking your ram. Since my ram is DDR2-800, and my current setup is at 850, that basically means that I just overclocked my ram by 50mhz. Some ram overclocks well while other types of ram do not. Any decent set of ram should allow a little overclocking headroom. In my BIOS on my 650i ultra motherboard, I used the "unlinked" and "sync'd" option.
 
yes i have my ram running at 850, because i have fast ram (ddr2 1066).

if you are serious about overclocking its always best to get faster ram, because chances are you ram won't overclock to well, faster ram always makes for easier more stable overclocking
 
Most DDR2 1000+ RAM is just DDR2 800 memory that was speed binned. Same ICC's just tested to go further than DDR2 800 speeds.
 
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