# Could someone explain 1:1 FSB:RAM to me?

#### cowspoo

##### Distinguished
I really.. i mean really don't get it .

CPU stock is at 266fsb
RAM stock is ddr2-667
( use these or make up your own examples) if i clock the cpu at 333fsb and set ram to 667 CPUZ says 4:5

How do tightening your timings from 5-5-5-15 to 4-4-4-12 change things?
What i know - ddr 2 667 = 667/2= 333mhz but it's dual channel.. so you divide it again by 2?
EDIT: I managed to get 1:1- Set FSB to 333, Set System DRAM to 533 which clocked it to 667-5-5-5-15
Now.. i'll go mess around and try to get 1:1 with System DRAM at 667

#### Evilonigiri

##### Splendid
Let's say you're running at 333MHz FSB. Then you want to run on 1:1 fsb to ram ratio. So now it's running at 333MHz ram. But since it's DDR2, you multiply by 2, giving you 667MHz. Dual channel has nothing to do with the speeds.

Let's say you're running at 333MHz fsb again. But now you set it to 4:5 ratio. You just do a simple equation, 333/? = 4/5 ?=416.25. Since it's DDR2, multiply by 2, giving you 832.5MHz for ram.

#### cowspoo

##### Distinguished
Thanks for the quick reply Evilonigiri! Okay so i understand that now. My BIOS doesnt have a ratio setting so i need to kinda do this by hand. When i raise the FSB.. the DRAM mhz raises by itself. I can set ____ manually
-fsb (266-513)
-system DRAM ( ?,533,667,800) ? = idk but don't need to worry about
CURRENT SETTINGS to make 1:1=333x8fsb, System DRAM 533. DRAM mhz 667, timings 3-4-4-11
To Optimize my ram usage i should run it at 667 through the system right? Then the mhz changes to like 832mhz basically there's no way to even it back out i'll try lowering the multiplier to raise the fsb

#### Evilonigiri

##### Splendid

You don't need to run at 667MHz, but if you want to, there's no issue there.

#### robertdv

##### Distinguished
But since it's DDR2, you multiply by 2, giving you 667MHz.

It's the same as DDR3 right?

#### Evilonigiri

##### Splendid

I would think so.

#### swair_xp

##### Distinguished
Hello
first of all , i need to know whether this cpu/ram ratio is that important or not,and how will i know what is my fsb ????
i am using the m3n-ht deluxe/mempipe asus mobo, i cant find the fsb online and i have not bought any ram i dont know how to achieve this ratio help please.....

http://www.asus.com/search.aspx?searchitem=1&searchkey=m3n-ht

#### iluvgillgill

##### Splendid
it is very important the ratio.anyway just set it to 1:1 and you will be trouble free.

#### Mondoman

##### Splendid
The CPU FSB:memory bus 1:1 *clock* ratio is only 1:1 for Intel CPUs and RAM running in dual-channel mode. Since on Intel systems all data to/from RAM goes through the FSB, you want the data throughput of the FSB to match the data throughput of the memory bus, so neither is a bottleneck.

Data throughput of FSB = FSB clock rate x 4 (that's why it's called "quad-pumped").

Data throughput of memory bus in dual-channel mode = individual DIMM throughput x 2 (two channels in parallel doubles the throughput).

Individual DIMM throughput = memory bus clock rate x 2 ("DDR" means double data rate).

Thus, to match data throughput of FSB and data throughput of memory bus, we get:
FSB clock rate x 4 = (individual DIMM throughput) x 2; expanding further, we get:
FSB clock rate x 4 = (memory bus clock rate x 2) x 2

This works out to:
FSB clock rate x 4 = memory bus clock rate x 4, or

FSB clock rate = memory bus clock rate, which is the famed 1:1 ratio!

Quick example:
For 1333MHz FSB throughput, FSB *clock* is 1333MHz/4 = 333MHz. Thus, for the 1:1 ratio here, we want the memory bus clock to be 333MHz, which is the same as running the DIMM modules at 333MHz x 2 = DDR2-667 speed.

#### one-shot

##### Distinguished
I actually just recently explained this to my friend....cept he had an old P4 2.8Ghz and 266mhz ram, lol. FSB with the 1:1 ratio got it OC'd to 3.3 at 1.55V. 21x Multi and did the math. My pc has a 450Mhz FSB and 450Mhz ram. 450Mhz*8 = 3.6ghz. It's a 1:1 Ratio, DDR2 doubled is 900 of course. just gotta do a little math. A divider of FSB-(4/5)-RAM = 1/1.25 Or your ram is 125% the speed of your FSB. 1:1 is whatever the FSB is your ram will be running the same speed and vice versa. Hope that helps

#### Evilonigiri

##### Splendid
For DDR2, you would multiply by 2. But for DDR3, would you multiply by 4? I think I just read that in graysky's Ocing guide.

On the side note, this thread is 5months old.

#### iluvgillgill

##### Splendid
damm!its older then my last phone!!!! time for a new one then!lol