CPU/Memory 1:1 ratio? What is it, and why do people do it?

Memnok

New member
During my research into hardware for my new computer build I have been spending lot's of time reading through reviews/message boards. I have seen several references to people running a 1:1 ratio. I believe they are referring to the CPU and memory speeds.

What is the benefit to running 1:1 ratio? Would this be an aggressive overclock, or more mid range?

Maybe someone has a link to a 1:1 tutorial?
 
What this ratio refers to is the direct relation of CPU clock cycles to memory clock cycles. So, in a 1:1 ratio situation the CPU and memory are running at the same speed. There are also other ratios that can be used that go both ways, memory running faster than the cpu and vice versa. They all have their benefits. A higher CPU:memory ratio is going to allow you to push your CPU clocks to the maximum without reaching an overhead on your memory. Whereas a higher memory:CPU ratio is going to give you top RAM speeds and more than likely not let you get the most out of your CPU clocks as you will run in to a memory speed wall much faster.

Hopefully this explanation was somewhat clear enough to understand. :p

Cheers. :beerchug:
 
Thanks, that does help clear things up.

But that leads me to another question...

Why is it that I see motherboards, memory and CPU's rated at high bus speeds, like 1033 and 1333MHz (or 1600MHz for DDR3), but when people talk about overclocking they can only reach top speeds of about 500MHz FSB?

This is all so confusing.
 
Ok, I think I found the answer to my own question:

KingCody said:
DDR2's effective speed (transfer rate) is double it's actual operating speed. if your FSB is set to 343MHz, then to achieve 1:1 your RAM would have to run at 343MHz as well (343MHz = DDR2-686).

your specific mobo/BIOS will determine how to achieve a 1:1 ratio:

if your BIOS lets you simply type in a target RAM speed then you simply change "auto" to "manual" and type in 343 (the BIOS will choose the appropriate multiplier/divider to achieve as close as possible to the target speed.

if your BIOS makes you select a ratio (listed as DDR2-533, DDR2-800, etc) than you'll have to calculate what the resulting ratio of each setting is. since the default FSB of an E6300 is 266MHz/267MHz, the 1:1 setting will always be DDR2-533. since the ratio doesn't change, if you set it to DDR2-533 and raise the FSB, the RAM will always operate in sync with the FSB (1:1)

NOTE: since your RAM is capable of running faster, then you should test different speeds (via benchmarks) to see what gives the best performance. you may benefit more from the extra bandwidth than with a 1:1 ratio.

I'm still trying to wrap my brain around this... I may have another question, but I'm not sure yet... :o
 
When you hear about 500mhz fsb this is becuase it is quad pumped so it would be 2000mhz on the fsb...

The cpu speed would be the fsb (500 in this instance) multiplied by the cpu multi. E.g. 500(fsb)*9(cpu multi)= 4.5ghz(cpu speed)

As you raise the fsb to overclock your cpu, your memory is overclocked too. How much it is overclocked is determined by the ratio/divider.

People set a 1:1 ratio as it overclocks the ram the least. This is done whilst you find your cpu's max OC. Once you find your cpu's max OC you can change the divider to crank up your ram.

It is then a case of finding a happy medium between the fsb and divider.

It sounds complicated, but it isn't. If you go into your bios you can set your fsb, then the divider/ratio (same thing) and see how your ram is affected.

I hope that didn't confuse the hell out of you because it's early and I'm not sure how clear an explination that is!
 
Hmmm, a side-note here. If i was running a pc, which would be a tiny amount above the 800mhz speed of my ram, what would i want to set my divider to, when using an AMD 5000+ black edition, on a bus speed of 200 mhz. If i went 1:1, would it be exactly 800mhz, as you quadruple the bus speed to get ram speed at 1:1? If so, then would 1:2 result in 400mhz on the ram or what?
 
1:1 of your FSB does indeed refer to the quad pumped one, so 1;2 FSB:Memory would be correct.

ex: 266fsb = 1066quad pumped

533 ram = 1066DDR

And there is your bandwidth limit.

I dont really do eithe rof that in my mobo I jsut set my ram to w/e I want fsb to w/e I want and it finds a happy divider, which is quite usefull.
 
Yeah, some good boards come with the "un-linked" option.. allowing you to set the RAM to what you want and the FSB to what you want.

Then it calculates the closest ratio and uses that.

Very clever in my opinion. :)
 
Okey doke, would that be the same on AMD 64?

If i was at a 200fsb (x16 for 2.6ghz) with 800mhz ddr2 ram, then would the ram quadpump to ddr800? which would be 400mhz, then i guess that as it is ddr2, it would bee ddr21600, which would be 800mhz, aka the top of my rams capacity.
 
DDR is aptly named for the way it works. Therefore they decided they'd claim it was twice the speed of SD before it. And doubled it again for DDR2.

200FSB at 1:1 is 200mhz REAL on the ram. Double it for the DDR = 400 and then the 2 = 800.

Its a big con really.
 
now why do you think then, that on a site i saw with ocing the 5000 black edition, when at 200fsb, it was abour 720mhz to start with, then 800mhz after increasing the multi a bit.
 
Its not what i think, that's how it works.

Link?

Altering the multi should have no effect on ram speed. They'd have to have adjusted the divider and/or FSB to alter the ram speed.
 
yes, but why does the ram (is "use" the term for mhz level?) increase when he ups the multi? is it because of the core voltage rising?
 
Urg, multiplier overclocking. Just to let you know out of a 400x8 and a 200x16 the 400x8 will be faster, dispite them being the same outright clockspeed (3200mh).

the dividers in that artical (as far as i can see form a skim) work a little different to what had been talked about previously. For better or for worse is debatable but anyway.

They say they changed the divider to 8 to obtain 1:1 with the FSB (200mhz, DDR-400, 2-800) because it used the total CPU frequency and divides it by the set number to obtain the RAM speed. It may just be that board or it may be a feature of the AMD IMCs, im not sure and can't be bothered to hook up my AMD rigs to check right now.
 
okey doke, thanks anyway. BTW, if i got my cpu to 3.2 with multi, then could i raise it above 3.4 using fsb too? or would it run into same stability problems as you would going to 3.4 with multi.
 
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