Question about faster ram and fsb:dram ratios with regards to overclocking.

[Apocalypse23]

Hi everyone, I was wondering about this for a long time but still am not sure how it works. If you could provide me with examples it would really help.

Right now i have my memory runing at 1:1 fsb:dram ratio which is great, its a ddr2 800 memory and my motherboard supports it. But what i don't understand is this:

The memory will run at half of its total frequency so CPU FREQUENCY X MULTIPLIER = proc speed.

so example 1:1 = 1/1 x cpu frequency = half the memory frequency so 445 in my case
2:3 = 3/2 x cpu frequency = still half the memory frequency? in whatever cpu frequency I set it to?

In my case it would be 445fsb x 9 multi = 4 ghz , so ddr2 800 is the max speed listed but im overclocking it to 445 x 2 = 890mhz total mem frequency right?

I am just wondering let say if I was to get pc2 1000 memory, my questions are:

1) My mobo lists memory supported as ddr2 667, 800, 1066 . It says it supports up to 1066 as well however I'm confused as to whether it will work with other frequency ram not on the list i mentioned......Or will it detect the pc2 1000 memory and automatically set the dram:fsb ratio? All this is done assuming i want 9 as a multiplier.

2)If i use ddr2 1000 for example, with my current configuration if i set the speed to 4 ghz and use 445 x 9, would i have to set the memory ratio to AUTO to let the computer find it's on suitable fsb:dram ratio? Would this be the optimal ratio or would i need to try my own settings? Also, do we just make up these numbers or is there a legit system to make dividings? i.e 2:3 3:4 5:6 7:18 ??? All this is done assuming i want 9 as a multiplier.

I just want to know how this really works and whether we leave the dividing part to the motherboard to figure out by itself and all we do is change the fsb and multis....

Thanks

 

[sutahz]

Every BIOS I've been in that lets you adjust dividers shows you what the new memory freq will be once you save and exit (so you know if your pushing your RAM past a known limit).
Intel cpu's these days quadruple the FSB. So with a 266MHz FSB the processor see's 1066MHz at its L2 cache (right?). But the muliplyer is based off the original FSB of 266 (266x9=2.4GHz).
AMD chips for the last long while have doubled the FSB.
DDR also doubles the FSB. So with a 1066FSB CPU, the actual FSB is 266, 266x2=533 so running your ram 1:1 you only need DDR2-533.

Very few applications benefit from running RAM on a divider to give it a higher operating frequency.

Im guessing the motherboard looks at the SPD of the RAM and puts the RAM on the appropriate divider so that when someone gets an application that tells them what speed their ram is running at, they see what they paid for (and it IS running at that freq).

 

[Tempered81]

if you put some of that ddr2-1000 in your board and boot auto, it would probably recognize it as ddr2-800 in bios. But knowing that it's capable of 1000mhz in spd (you can check cpuz mem tab or spd tab for cas settings) you can comfortably choose a FSB speed of up to 500mhz and keep a 1:1 ratio. This way your memory is not overclocked, but running at 1000mhz. You could try 8x500 for 4000mhz assuming your mobo/e8400 can handle it. This also gives you a lot of ease when running the 9x multi and looking for safe FSB speeds of between 400-500mhz. You wont be overclocking them memory like you are now.

Yes in your current setup you run the memeory at 445 mhz which is a 1:1 (lowest) divider and the mem actually runs at 2x445 or 890mhz. You've a 90mhz oc on the mem, stressing it and possibly require more latency. the cpu is running at 445x9 or ~4000mhz. 445=ram, fsb frequency. 4000=cpu freq, 9 = divider, 890 = dual channel rated mem freq (445x2).

say you had your ddr2-1000 and ran your e8400 & mobo at stock settings of 333mhz FSB. You could easily use a 3:1 mem divider and that memory would run at 999.9mhz or 1000mhz which is its rated speed. This way you are getting the most out of the ram. (this is the scenario where people say the performance gains in real life applications are little if any at all) The true advantage of having quick memory in your situation is allowing for the 500mhz FSB comfortably.

 

[brencat]

Originally posted by: jaredpace
say you had your ddr2-1000 and ran your e8400 & mobo at stock settings of 333mhz FSB. You could easily use a 3:1 mem divider and that memory would run at 999.9mhz or 1000mhz which is its rated speed. This way you are getting the most out of the ram. (this is the scenario where people say the performance gains in real life applications are little if any at all) The true advantage of having quick memory in your situation is allowing for the 500mhz FSB comfortably.

Math error there...

DDR2 1000 = PC2-8000 = 500 mhz rated RAM.

Hence, max divider to keep RAM at stock would be 2:3 (i.e. 333 FSB: 500 RAM)

RAM would most likely go higher with relaxed timings and higher vDIMM so you might be able to get away with a 3:5 divider (i.e. 333 FSB: 555 RAM). Much higher however, and you'd likely have to go to PC2-8500 (rated for 533 mhz)

The easy way to cut through the marketing language:

When you see RAM marketed as "PC2-8500"...divide by 16 = ~ 533 mhz rated RAM
When you see RAM marketed as "DDR2-1066"...divide by 2 = ~ 533 mhz rated RAM

 

[Tempered81]

Originally posted by: brencat

Originally posted by: jaredpace
say you had your ddr2-1000 and ran your e8400 & mobo at stock settings of 333mhz FSB. You could easily use a 3:1 mem divider and that memory would run at 999.9mhz or 1000mhz which is its rated speed. This way you are getting the most out of the ram. (this is the scenario where people say the performance gains in real life applications are little if any at all) The true advantage of having quick memory in your situation is allowing for the 500mhz FSB comfortably.

Hence, max divider to keep RAM at stock would be 2:3 (i.e. 333 FSB: 500 RAM)

oops. thanks

 

[Tempered81]

Originally posted by: brencat

Math error there...

When you see RAM marketed as "DDR2-1066"...divide by 2 = 531 mhz rated RAM

 

[brencat]

You got me...

533mhz D'oh!

 

[Apocalypse23]

Ahhh, thanks you so much guys, really helped me clear the analogy.

My only question now is this:

Will it be advisable to buy faster memory and not overclock it, but only overclock the cpu? Is that what the main benefits of faster memory are with regards to overclocking? But also, this will be done using different multipliers I take it, so if a e8400 for example has a 9 stock multiplier, is that the best one? How off can i go with settings for multis, like the gentleman mentioned above about 8*500 to give me 1:1. Will the 8 hinder performance? I've read that it makes literally no difference in different multis and fsbs as long as you get the same speed....and also for ratio's I need to confirm what would be more advisable, i.e 1:1 or something a little different and does it make any real difference?

Another question is this: Wouldn't the mobo be having difficulties hitting 500 fsb? Because am i not using 8*500 and then pushing the mobo to help raise to that fsb? I keep hearing about mobos and how they need to reach the highest fsb etc, does that imply to this?


"The easy way to cut through the marketing language:

When you see RAM marketed as "PC2-8500"...divide by 16 = ~ 533 mhz rated RAM
When you see RAM marketed as "DDR2-1066"...divide by 2 = ~ 533 mhz rated RAM "

so what would be more advisable, pc1066 since it's higher? or pc1000? or is the difference pretty much neglegible?

I am asking this because I am also planning to build a Qx9650 but I want to put enough juice in it so you can overclock it to much higher than just using ddr2 800 . And all this is to be done no a 780i motherboard as well since it will be a 3-way sli configuration.

Thanks so much!

 

[brencat]

Generally, it is preferable to run C2D chips at their default multi and OC with the FSB. This allows you to enable C1E and EIST if you so choose. They don't work properly at non default multipliers. There is a negligible difference between 9 x 445 and 8 x 500, likely noticeable only in benchmarks. With intel chips, core speed is king.

Therefore, depending on what CPU you're buying and what your target OC is, you should buy RAM appropriately -- as opposed to over-buying. Example: you buy an E8400 which is a 9x multi CPU and your target OC is 4ghz. So, that means a FSB target of 445 mhz. Most decent PC2-6400 (400mhz rated RAM) is capable of 475 - 500mhz at CAS5. However, if you must run CAS4 in said situation, then it is generally advisable to buy something like PC2-8500 (533mhz rated) and run it underclocked 1:1 @ 445 mhz. Then it might be capable of tighter CAS4 timings.

Frankly, IMO it's not worth the extra money for the better RAM if all you're doing is trying to go from CAS5 to CAS4. Approaching 500 FSB is nothing to shake a stick at either considering the stress it puts on the mobo and RAM.

Finally to your last question about dividers, at FSB speeds over 400, most people run 1:1 or 4:5 dividers for everyday use. Beyond that, you're really pushing your RAM hard and/or needing 2.2 - 2.3+ vDIMM to get there which isn't advisable for 24/7.

 

[Tempered81]

I would agree most people with decent 800mhz ram aren't going to need pc2-8500 unless they're trying to push over 450mhz FSB. For your qx6850 you can set the bus at 400mhz and keep the ram at 1:1 with pc2-6400 because it has an unlocked multiplier. This means you could just up it from 9x to 10x and go from 3600mhz to 4000mhz. The advantage of the extreme processors this go-round. ''

 

[sean2]

Originally posted by: jaredpace
I would agree most people with decent 800mhz ram aren't going to need pc2-8500 unless they're trying to push over 450mhz FSB. For your qx6850 you can set the bus at 400mhz and keep the ram at 1:1 with pc2-6400 because it has an unlocked multiplier. This means you could just up it from 9x to 10x and go from 3600mhz to 4000mhz. The advantage of the extreme processors this go-round. ''

I have the basic config of a vostro 1400
T5270
2 X 5200 677
wifi n dell
bluetooth
webcam
120g hd

I hope to install red hat or centos and a have a few MS os up and not including vista
I have defaults mem of 677 - with 2 - 1 gig, shiped with unit taking both slots, I would like to upgrade this as there might be both 64 bit linix and 32 MS os's running under virtulization either red hat current version native the rest as guest, or xp host the rest as guest. I am told that xen does not support any intel under t7000 series, however sun recently acquisition of virtualbox.org does.


I would only upgrade to t7000 series cpu when it is dirt cheap,


I hope you can help in a decision I need to make:
is it worth it to buy 800 vs 667 or even faster memory that the vostro can handle saftly, what will be the fastest supported and is it worth it
thanks in advance for your help

further is their any reports of successful running redhat must current RHEL on vostro 1400 ( I have seen about fedora and audio solution, (I am not sure about wifi N driver) links to such url will be great, so I know from the start, all the get around's.