Can someone explain ratios for me 3:4 1:1 4:5 ??

Can someone explain ratios for me 3:4 1:1 4:5 ??? I want to know what people are talking about when they say they are running at 4:5 or 1:1

Also known as the CPU : DDR ratio.

1:1 - 133mhz fsb - 266mhz DDR (2.00x)
3:4 - 133mhz fsb - 333mhz DDR (2.50x/2.66x)
4:5 - 133mhz fsb - 400mhz DDR (3.33x)

-PC

are you sure on that last one, cullam3n?

sorry if your right lol.

If your running a 133 Bus and you wanna run your ram higher you would use a divider.
133 FSB using 3:4= 177 MHZ (177X2) memory bus
133 FSB using 4:5= 166 MHZ (166X2) memory bus

james.miller said:

are you sure on that last one, cullam3n?

sorry if your right lol.

Click to expand...

I'm probably wrong, those were off the top of my head.

-PC

I think that one bit of info is wrong.

I don't think it's CPU : DDR ratio

I always though it was FSB : Memory Bus ratio.

So, a 133 FSB with a 1:1 give a 133 Memory Bus (which DDR makes it effectively 266Mhz).

A 150Mhz FSB with a 4:5 ratio would make the Memory Bus 187.5Mhz (DDR making it 375, ie, close to PC3200).

But then again, maybe I have it wrong. Hopefully someone who is more knowledgable than me can shed some light on this.

yes you got it right!! if i'm not mistaken it goes 187.5X2X64/8=PC3000

What kinda ram do you plan to overclock?

Here is a link to a post I made recently that goes into a little detail about memory ratios and multipliers. It is in response to a user running a 176MHz fsb, so it uses this figure for the example demonstrated. Feel free to apply it to whatever fsb is of use to you.

http://forum.oc-forums.com/vb/showthread.php?s=&postid=1303823#post1303823

One minor clarification, we tend to say the cpu:memory ratio, but in reality we are talking about the FSB:memory base frequency relationship. I need to start phrasing it this way as it avoids confusion. The FSB gets multiplied by the cpu's multiplier, and the base frequency of the ram gets multiplied by the memory's multiplier (2X in the case of DDR, with RDRAM allowing us to vary the multiplier between 3 and 4).

Right after X-mas I'm planning on buying a 512 of XMS 3200 or 3500 to OC a 1.8a on an Asus P4PE. I wanted to learn about the different settings before I started OCing this new setup.

Why would you want to change this ratio? What is the benefit of running 3:4 instead of 1:1 ? Why do some ratios work for some people and others dont?

iceman2g said:

If your running a 133 Bus and you wanna run your ram higher you would use a divider.
133 FSB using 3:4= 177 MHZ (177X2) memory bus
133 FSB using 4:5= 166 MHZ (166X2) memory bus

Click to expand...

Forgive me for being stupid,
but why are you INVERTING the ratio (changing 3/4 to 4/3) when multipling by the FSB ?

I know you have to do it for the math to work, but why?

He's not inverting the ratio.

If the ratio of FSB:RAM is 3:4 then if the FSB is 100 then the ram is 133. Same goes with the higher numbers.

Falkentyne said:

Forgive me for being stupid,
but why are you INVERTING the ratio (changing 3/4 to 4/3) when multipling by the FSB ?

I know you have to do it for the math to work, but why?

Click to expand...