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difference between fsb OC'ing and using multipliers? - Page 2

post #11 of 18
Thread Starter 
I understand how to OC better now. but if you raise the fsb do u hav to raise the ram's mhz to make them equal? if you dont then wouldn't setting a FSB:RAM ratio b the best thing to do after upping the FSB
post #12 of 18
Quote:
Originally Posted by Kill2Fill View Post
I understand how to OC better now. but if you raise the fsb do u hav to raise the ram's mhz to make them equal? if you dont then wouldn't setting a FSB:RAM ratio b the best thing to do after upping the FSB
The RAM's speed will go up with the bus whether you use a RAM divider or not. What you are setting with a divider is a ratio between the bus and RAM speed reached - It's not a matter of raising your RAM speed since it happens anyway when bus speeds go up.

Know how the engine in your car will rev up some, then the trans will change to the next gear and the engine RPM's drop to keep the engine from revving too high? That's what RAM dividers are for, they are essentially "Gears" for your RAM to keep them within an acceptable MHz range. The larger the divider used, the slower the RAM will run in relation to your bus and that ratio or difference remains consistent until you change the divider again yourself.

For example if using regular DDR based systems, a 1:1 ratio means both the RAM and bus run at the same speed.

If this is based on standard DDR, that would be 200MHz for both but if using a 166MHz divider, then the RAM runs at 166MHz while the bus itself is at 200MHz = 34MHz slower than the bus. This 34MHz difference remains consistent no matter where you set the bus itself so that means you'd need a setting of 234MHz on the bus to get your RAM back up to 200MHz.

This is the same for all dividers used and it works the same for all of them.

A 133 divider will run the RAM at 133MHz with the bus at 200MHz, this means your RAM is now running 67MHz slower than the bus, again this difference is consistent. With a 133 divider used, you'd now need a bus speed of 267MHz to get your RAM up to 200MHz.
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post #13 of 18
Thread Starter 
so your saying that if wer 2 change my FSB i wouldn't need to change the RAM because the divider would change it itself? and that the RAM speed and FSB speed dont need 2 b equal?
post #14 of 18
ex. with a 3ghz cpu and 1600 ram, 2000 ht with 200 fsb


if you overclock the fsb to 205
cpu = 3.075, ram = 1640, ht = 2050

if you overclock via multiplier
cpu multi from 15 to 15.5
cpu = 3.1, ram = 1600, ht = 2000
post #15 of 18
Quote:
Originally Posted by Kill2Fill View Post
so your saying that if wer 2 change my FSB i wouldn't need to change the RAM because the divider would change it itself?
In most cases that would only happen if you have the divider option set to "Auto" in the BIOS. The board itself would then manage your divider settings. Sometimes the board will drop it anyway if RAM speeds get too high.


Quote:
Originally Posted by Kill2Fill View Post
...and that the RAM speed and FSB speed dont need 2 b equal?
No they don't need to be and in fact using RAM dividers lets you go further with the bus. RAM typically does not clock as high as your bus can and that's why slowing the RAM down with a divider is handy. Dividers keep the RAM within it's operational limits.
Again using standard DDR as a point of reference, many sticks of DDR can reach 230MHz stable no prob - Some can go higher, say about 250MHz or better and even a few can hit 300MHz with the right settings and tweaks.

Since most OC'ing boards can go at least 300MHz or better on the bus itself, you have to run a divider to keep the RAM from overspeeding itself. Also note I used the term "Stable", RAM will get unstable if it's speed gets too high and you'll begin having all kinds of problems if it does such as BSOD's, random lockups and outright crashes of the system.
Every stick of RAM of course has a limit to how high it can go before this becomes an issue. By using the correct divider, you can keep it within this MHz range to ensure it will remain stable.

For example, if your RAM tops out at 250MHz, to go higher on the bus you'd need to run a divider BEFORE raising the bus higher than 250MHz since your RAM itself tops out at 250.
It would be OK to use a 1:1 setting with it until you hit 250 on the bus, then you'd need to run a divider to go higher with the bus with these same sticks of RAM. This will then drop the RAM speed below the 250 threshold so you can keep raising your bus beyond 250MHz. If you raise bus speeds to the point your RAM once again hits 250, then you'd run an even lower divider to continue raising bus speeds - It's all about managing RAM speeds with dividers to keep your RAM within it's own operational limits.
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post #16 of 18
Thread Starter 
Quote:
Originally Posted by ffejrxx View Post
ex. with a 3ghz cpu and 1600 ram, 2000 ht with 200 fsb


if you overclock the fsb to 205
cpu = 3.075, ram = 1640, ht = 2050

if you overclock via multiplier
cpu multi from 15 to 15.5
cpu = 3.1, ram = 1600, ht = 2000
what's HT?
post #17 of 18
Thread Starter 
and thanks kryton and ffejrxx
post #18 of 18
HyperTransport
its the speed that the cpu talks to its cache

athlon ii and phenom ii (x2/x3/x4), max around 2000, will go slightly faster, but not very much
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