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The ol' 1:1 FSB/RAM ratio 'myth'

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March 31, 2009 11:57:58 PM

I've been doing some research into overclocking and I find that a lot of people are saying that a 1:1 ratio is not the ideal ratio, and that the higher the speed of the RAM, the better. However, if the CPU and RAM are both communicating with each other, would it not make sense to do so at the same clock speed? I don't see the benefit of running RAM at a greater speed than the CPU as the CPU would simply act as a bottleneck.

Any light shed on this would be much appreciated.

More about : fsb ram ratio myth

a b K Overclocking
a b à CPUs
April 1, 2009 12:14:25 AM

From the following thread - http://www.tomshardware.com/forum/247906-29-ratio#t1781...

Ah, but wait... there's more! :pt1cable: Let's consider some of the additional variables involved in the memory big picture: :o

A ratio of 1:1 provides the best level of stability, since the memory controller, which is an integral part of the northbridge chipset for Intel processors, does not need to translate data flow across the FSB between the memory modules and the processor(s). Also, since memory and processor FSB clocks are synchronous at 1:1, (400:400 or DDR 800), there is no additional latency introduced.

If a minimal ratio of 4:5 (400:500 or DDR 1000) is used, then the resulting increase in memory frequency is effectivey cancelled out by the latency introduced in translation across the FSB between memory and processor clocks, and no increase in memory performance can be noticably detected in benchmarks. Also, asynchronous or mismatched clocks create an element of potential instability within the memory controller, so depending on the chipset, an increase in northbridge and memory voltage is required for stability, which results in more heat, and less FSB overclock ceiling.

If a more aggressive ratio of 2:3 (400:600 or DDR 1200) is used, then the increase in memory frequency can marginally overcome the latency introduced in translation across the FSB between memory and processor clocks, resulting in a marginal increase in memory performance, which typically yields an increase in memory benchmarks of 2 to 3%, and is relatively negligible in terms of overall system performance.

In the case of DDR3, where a ratio of 1:2 (400:800 or DDR 1600) or 2:5 (400:1000 or DDR 2000) is used, even with the tightest timings, an increase in memory benchmarks of only 3 to 4% is yielded over DDR2 800, which once again, is relatively negligible in terms of overall system performance. It's also noteworthy to consider that DDR2 memory timings of 4-4-4-12 compared to 5-5-5-15, will yield an increase in memory benchmarks of less than 2%. However, for those of us who have the need for speed, we'll take whatever we can tweak.

Additionally, at equal specifications, 4 memory modules offer less FSB overclock ceiling than 2 modules, since more northbridge and memory voltage is required to maintain stability, and 4 slots require twice the current of 2 slots, again resulting in more heat, which typically is pulled into the CPU cooler, where it can increase processor temperatures by a few unwanted degrees.

I hope this helps to provides a greater degree of perspective (no pun intended). :D

Comp :sol: said:
Ah, but wait... there's more! :pt1cable:  Let's consider some of the additional variables involved in the memory big picture: :o 

A ratio of 1:1 provides the best level of stability, since the memory controller, which is an integral part of the northbridge chipset for Intel processors, does not need to translate data flow across the FSB between the memory modules and the processor(s). Also, since memory and processor FSB clocks are synchronous at 1:1, (400:400 or DDR 800), there is no additional latency introduced.

If a minimal ratio of 4:5 (400:500 or DDR 1000) is used, then the resulting increase in memory frequency is effectivey cancelled out by the latency introduced in translation across the FSB between memory and processor clocks, and no increase in memory performance can be noticably detected in benchmarks. Also, asynchronous or mismatched clocks create an element of potential instability within the memory controller, so depending on the chipset, an increase in northbridge and memory voltage is required for stability, which results in more heat, and less FSB overclock ceiling.

If a more aggressive ratio of 2:3 (400:600 or DDR 1200) is used, then the increase in memory frequency can marginally overcome the latency introduced in translation across the FSB between memory and processor clocks, resulting in a marginal increase in memory performance, which typically yields an increase in memory benchmarks of 2 to 3%, and is relatively negligible in terms of overall system performance.

In the case of DDR3, where a ratio of 1:2 (400:800 or DDR 1600) or 2:5 (400:1000 or DDR 2000) is used, even with the tightest timings, an increase in memory benchmarks of only 3 to 4% is yielded over DDR2 800, which once again, is relatively negligible in terms of overall system performance. It's also noteworthy to consider that DDR2 memory timings of 4-4-4-12 compared to 5-5-5-15, will yield an increase in memory benchmarks of less than 2%. However, for those of us who have the need for speed, we'll take whatever we can tweak.

Additionally, at equal specifications, 4 memory modules offer less FSB overclock ceiling than 2 modules, since more northbridge and memory voltage is required to maintain stability, and 4 slots require twice the current of 2 slots, again resulting in more heat, which typically is pulled into the CPU cooler, where it can increase processor temperatures by a few unwanted degrees.

I hope this helps to provides a greater degree of perspective (no pun intended). :D 

Comp :sol: 
a b K Overclocking
a c 87 à CPUs
April 1, 2009 12:17:39 AM

And here I was thinking that after "doing some research into overclocking" you might be able to talk to us about this. Instead you just want a bunch of people to random give their opinion? What did your research tell you? If you already did it, you should be able to tell us the results. (or at least link to a page and ask if your interpretation is right.)

For the record, faster ram does equal faster X. The problem is a lot of the faster ram doesn't provide enough extra X to make it worth the price you paid. For example, if you can buy DDR2-800MHz ram and get 60FPS in game X and it costs you $35 after rebate, why buy DDR2-1150MHz ram that gets you 63FPS and it costs $70? Double the price you paid while giving only 3 more FPS?
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April 1, 2009 7:18:34 PM

4745454b said:
And here I was thinking that after "doing some research into overclocking" you might be able to talk to us about this. Instead you just want a bunch of people to random give their opinion? What did your research tell you? If you already did it, you should be able to tell us the results. (or at least link to a page and ask if your interpretation is right.)

For the record, faster ram does equal faster X. The problem is a lot of the faster ram doesn't provide enough extra X to make it worth the price you paid. For example, if you can buy DDR2-800MHz ram and get 60FPS in game X and it costs you $35 after rebate, why buy DDR2-1150MHz ram that gets you 63FPS and it costs $70? Double the price you paid while giving only 3 more FPS?


I wasn't hoping someone could give their 'opinion'; I was hoping that there was someone out there who knows how this works and enlighten me on why this is the case. I have seen benchmarks and it does seem that the 1:1 ratio proves inferior to the other ratios. That's why I asked.
a b K Overclocking
a c 87 à CPUs
April 1, 2009 9:23:50 PM

Based off your research, how is it "inferior"? What did I write and Comptronix quote?

I'm not even sure exactly what your asking. 1:1 is good because the math is easy, the parts are cheap, and the performance is ~95% of what faster speeds can bring. If you can ask a specific question other then "Any light shed on this would be much appreciated." we might be able to better answer.
a b K Overclocking
a c 87 à CPUs
July 11, 2009 10:00:17 AM

I prefer something like this as a link.

http://www.anandtech.com/memory/showdoc.aspx?i=2916&p=6

Notice that while the FPS do go up as memory speed increases, its not like your getting a whole lot more. For example, looking at the top line (OCZ) for Farcry, moving from DDR2-800 to DDR2-1066 gets you an extra 2.4FPS. When you're already getting over 100FPS with either case, this isn't going to be noticed. As a percentage, thats around 1%, or 2%? This is why I claim that buying faster ram, or running the ram faster then the FSB really isn't worth it.
a c 197 K Overclocking
a c 172 à CPUs
July 11, 2009 7:39:26 PM

"A ratio of 1:1 provides the best level of stability, since the memory controller, which is an integral part of the northbridge chipset for Intel processors, does not need to translate data flow across the FSB between the memory modules and the processor(s). Also, since memory and processor FSB clocks are synchronous at 1:1, (400:400 or DDR 800), there is no additional latency introduced."

The improvement in stability, especially in high overclocks, is more than worth the unnoticeable (except for benchmarks) increase in memory i/o.
November 13, 2009 11:23:15 AM

i am sooo bloody confused:( 

heres my take, and i hope some one can assist me ...

my pc is e6700 C2D 2.66ghz on a 266mhz fsb qud to 1066mhz - cpuz
my ram is a-data 6400 (cl5) but apparently it detects as 5-5-5-18 ? not 15??mmm , ddr2 400, dual channel @ 800...
555/15 doesnt seem to work , freezes on boot
444/12 does tho ... @ 533

base on a few threads i read.. i become confused...
my mobo cmos allows me to set the ram to 533/667/800
i can;t change cpu tho, 2.66 x 10 ...

if i understood 1:1 term and stability issue
my ram should then be set to 533 dual channel = 266x2 ?
or did i have the wrong rams ? and should instead get ddr2 533 instead of my current ddr2 400 ?? which in dual mode should net me 1066 == 1:1 with my cpu "rated" fsb ?

OR ??

if i downgrade my current ram to 533 , = 266x2 , it becomes 1:1 with cpu ?? bus speed ?

but if i think i calculate it correctly then my cpu fsb:ram would be 1066: 533
would be 2:1 instead ?? or is this wrong ?
or 1066:800 (current setting) ? would this be better??

i did a test using sisoftware sandra...
444/12 - 4.7 mb/s
auto(555/18) - 5.476 mb/s (which means non 1:1 = faster)

is there any way to improve performances ?
a c 197 K Overclocking
a c 172 à CPUs
November 13, 2009 3:10:24 PM

No. Simply change your Memory Clock Multiplier (or whatever your BIOS calls it) from AUTO to 2.00.

That way your memory clock will always be twice your FSB frequency.
November 14, 2009 4:05:44 AM

mmmm i dun think i have that option in my bios .. :( 
a c 197 K Overclocking
a c 172 à CPUs
November 14, 2009 9:07:34 AM

There's a very good chance that you do have this option, but you do not recognize it.

What kind of motherboard?
November 14, 2009 10:35:51 AM

MSI MS-7235 INTEL P965/G965, Rev1.1. C1
Bios: Phonenix Technologies, V6 PG, 07/05/2007

info from CPU-Z..

the mobo has a built in dynamic clocking but provides no way to change the multipler... the DOTs iirc ,, provides "army" based callsign for each different levels of OCing,, but provides no details how much it overclocks to -.-'
eg: private , sergent, blah blah cant rememebr all of them


there is manual options to change ram latency..
open values are 3to5 , 3to6, 3to6, ? to 15 (no 18 for sure)
when set to manual i can change the fsb of the ram to 533/667/800
other than that i dun see any other settings
i heard of a hidden ctrl + f1 menu
doesnt sseem to in cmos anywhere, or that i do not know where to activate it.. or maybe msi doenst have it..

as mention i change to 533 which should be 1:2 (bus : ram) or 2:1 (rated fsb : ram)

but in 533 mode, Sandra reports 4.5 mb/s bandwith in 800 mode, sandra reports 5.4 mb/s bandwidth..

so i'm kinda confused,, faster or stable ?
althought it works fine most of the time, only occasionally it just freezes up for no reason
a c 197 K Overclocking
a c 172 à CPUs
November 15, 2009 10:39:33 AM

babyoxide said:

only occasionally it just freezes up for no reason

"only occasionally it just freezes up for no apparent reason"

a b K Overclocking
a b à CPUs
November 15, 2009 10:47:33 PM

If it doesn't freeze when set to 533, thats your answer.
I found on my Asrock P45, overclocking + memory multipliers were not a good idea. On the Gigabyte P45 it was party-time.

So quality/board design and the chipset both can have an effect on how reliable a multiplier is.
!