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Question about FSB / Memory freq...

Last response: in Overclocking
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December 7, 2009 8:33:53 PM

I recently built the following machine...

Asus M4A79XTD MB
AMD PH II X4 955 3.2ghz
Sunbeam freezer with AS5
Saphire Radeon 4890
4gb Gskill DDR3 1600
1 TB Seagate HD
Antec 300 case with extra fans (all air exiting the case is cool)
500w Thermaltake psu

I understand that these cpus dont have a FSB, but rather a onchip memory controller (which ONLY talks to the memory, right?), and a HyperTransport (which talks to nb/everything else). So question 1...

1.) In my bios, I have a option for CPU BUS Freq. I assume this is how I control the freq of this 'memory controller'?

Assuming that is correct, my next question is...

2.) Since my DDR31600 memory should operate at 800mhz (base), if I dont set my CPU Bus Freq to AT LEAST 800hz, arent I bottlenecking communication between my cpu and ram? I understand you CAN use different freq ratios between cpu and memory, they dont have to be 1:1. But I want my memory to run at 800hz, so doesnt my "CPU Bus Freq" HAVE to be set at 800hz as well? However, if I recall my CPU Bus Freq didnt even have an option to go that high.. it could only go 200-600...

And last question...

3.) I have heard mixed reports that modifying my "CPU Bus Freq" will also effect my HT/NB speeds. That doesnt make any sense, since I thought we were just dealing with the onchip MEMORY controller here... I mean my HT has its OWN independent setting in my bios, so you think the two wouldnt be tied together. Cananyone confirm/ deny?

Thanks!
a b K Overclocking
December 7, 2009 10:00:46 PM

Changing your FSB frequency overclocks the whole system including the memory. So if you raise your fsb to speed up your cpu it also overclocks your ram among other things. This is why cpus with unlocked multipliers are better, you can increase the multiplier instead of the fsb so it only effects the cpu.

And if you over clocked with your fsb you might have to turn down the speed of the ram to get it to function correctly. That is one of the down sides to over clocking using FSB, sometimes you are limited to the most limiting thing in the system, not the cpu.

Based on what I just read in your post I suggest you study some of the basic over clocking guides some more before you even attempt to OC your system. If you max your FSB out all in one shot lets just say I hope you have been saving up for new computer. Because you might need one.

Over clocking is something that takes time and lots of messing around, even if you know what your doing. For those of us that are new to it we have to be extra careful.

Change one setting a small amount at a time and test it to see what happened. Its a very long process sometimes. And sometimes not worth the gain or the stress on your system in the end.

Lets use my system as an example. I have a X2 240 2.8 cpu on a biostar board with 4 gigs of pny ram. Nothing real fancy and not real expensive. Maybe 70 bucks for the cpu, 60 or so the for the mother board and I think I got raped on the ram but lets say another 100 bucks for the 4 gigs of matched ram. Then if you plan on overclocking you need an aftermarket heat sink and possibly some extra fans and or a decent case for good cooling. Better ram rated for overclocking wouldn't be a bad idea either.

Lets say I want to really mess around and throttle this thing up. I have seen people say they can get 3.7 out of a 240. I could actually only get 3.5 out of mine though. So I see this guys post about his fantastic over clocking job and just copy his setting, or I do some simple math on what my fsb setting should be for 3.7. After all his could do it right? Things go wrong and I end up frying my 70 dollar cpu and ram, and if I am lucking not my motherboard.

Now I have to replace them which is going to be around 150 bucks or so if I stick to what I had and my mobo is still good. More if I decide to upgrade.

Opposed to if I wanted a 3.0 system or higher I could have gotten the phenom X4 965 that is a quad core rated at 3.4 gigs and its a black edition with an unlocked multiplier. These sell for under 200 dollars and would outperform the over clocked 240 right out of the box, no fuss no muss.

And the worst part, when I over clocked my system to 3.5 it benchmarked pretty but really didn't notice a difference in real world performance for what I use my computer for. So risked ruining my system for something that really didn't even help me out. Pretty smart huh.

Something to think about anyway.

And I know what you thinking:

"Shut up dad!"

LOL

Paul
December 7, 2009 10:35:25 PM

Quote:
Changing your FSB frequency


A64 chips dont have a FSB. This was the whole point of my post. Or perhaps you could say they have TWO fsbs. They use a HT bus for all NB communication, and a dedicated on chip controller exclusively for the memory (or at least I assume its exclusive).

But in any case, my question is still valid -,How can you NOT bottleneck your system if you dont run your fsb/memory controller at 1:1 frequency with your ram. Which in my case, would require me to clock my "CPU Bus Frequency" (thats what its called in the bios, and I assume thats my onchip memory controller) to 800mhz. How else could the cpu keep up with my ddr3 1600 ram.
Related resources
December 8, 2009 1:58:36 AM

And assuming the 'Core Bus Freq' effects more than just the memory bus, can anyone explain what all it DOES effect? I imagine just the HT and as a direct result the NB right? Well if thats all it does, why does everyone suggest to leave your fsb at 200hz, and just up the multiplier cpu core multiplier? Wouldnt it make more sense to up the fsb to something like 400hz (so you get better memory performance), then just UNDERCLOCK the ht/nb, if it cant handle that high of a fsb?
December 11, 2009 3:13:57 PM

my ram is at 800mhz, and my fsb is at 200mhz, its a 1:4 fsb to dram.

if you up the fsb, youre going to have to reduce the multiplier. but like stated its going to change the ram because its going to try and keep a ratio.

for example.

at my current settings the ram is at 800mhz
and the fsb is at 200

if i move the FSB to 250, the 1:4 ratio would mean that the ram would now work at 1000mhz. this is a signifcant boost in the ram speed, i would also have to up the voltage of the ram probably to keep pace, and also change timings.


BUT

if i just change the multiplier, that means the FSB and memory ratio stay the same.


-------
but what if you reduce the ram speed?

667 mhz instead of 800
and the fsb is at 200

the ratio is a 3:10

but again it will have to keep pace.

at 250mhz X 10 = 2500


the ram would now have to operate at 833 mhz.

you see your ram has to over clock significantly to attain the higher speeds, whereas with the multiplier the ram doesn't take the beat down.

You see they have to operate in tandem so the ratios have to meet at some point. in the second case a 3:10 ratio means that the point the two numbers meet is at 2500mhz. so 250x10 and 667x3 both equal = 2500.


because my 955 works at 3.2 ghz 200x 16 = 3200
I dont know i mean on paper it sounds like you could do 400x8 = 3200, and then the dram:fsb would be 1:2, but would there be a gain to that? and can the CPU support a 400 mhz FSB at that multiplier?
a b K Overclocking
December 13, 2009 3:30:57 PM

I really don't know how to explain this so you will understand it. You are confused on how this works. You don't need to change anything. If your FSB/core bus frequency is at 200 and you have 800 ram its already running at 800. Use cpuz and check it. It automatically sets when you install the ram and boot the machine. Oh and cpuz will read half the speed so don't let this confuse you. 800 ram will read as 400 you need to double it to get the correct frequency.

On some motherboards you can adjust the memory separate if you want, like change the multiplier or the speed to over clock or under clock it. But the point is if its set to auto you don't have to do anything. With fsb set to stock the memory controller in your cpu is already set to the correct setting for your memory.

The only time you have to mess with this is if you were to overclock your cpu using the fsb/core bus frequency and making the frequency higher. Since this will over clock the whole system including your ram. If you raised it high enough you would have to under clock the ram possibly to make it run stable. Like use a lower multiplier or set the ram back one setting. Without looking at my bios I forget the exact the numbers.

But, yes you could over clock your memory this way. You could raise fsb frequency and lower the multiplier for your cpu. This would raise the rest of your system yet keep your cpu frequency lower. Why you would want to do this I have no clue since you will probably see no performance gain from it. CPU speed will show much better gains than memory over clocking will. At least in my experience. From what I have read you are actually better off with slower speed and tighter timings on your ram. I have yet to mess with my ram though.

I would rather over clock the the cpu and under clock everything else if I had to. I have never noticed ram speed to have a big overall impact on performance for me. Its the last thing I worry about to be honest.

And the numbers you are talking about are crazy high. Doubling your fsb from 200 to 400 is insane, if your computer will even let you do it. Raising your fsb to 230 or 240 will darn near put 800 ram at 1000. Put it at 400 and I doubt it will even boot up.

And I am not sure the cpu multiplier effects ram either, I think its separate. Like say my cpu's multiplier is 14x, its locked for raising but I can lower it. But if I lowered the multiplier I don't think it would lower my ram speed as well. Because when running in power saving mode my multiplier drops quite a bit but my ram speed remains the same. According to cpuz anyway. Never tried to manually lower my cpu multiplier to be honest though so I can't say for sure how it effects it. Maybe if I get time I will mess with it.

Paul
December 13, 2009 7:37:08 PM

from what ive come to understand on AMD systems you cant really touch the Reference frequncy. Youre stuck at 200mhz becuase the whole system including the NB runs at that. If you touch it a bit the system will probably go wonkie. There is probably a TINY bit of room to up the frequency, but not much.. maybe 210-215, and youd be at the upper edge of stability. Everything gets over clocked when you do this - the entire system, so expect more heat, less stability, etc. And from what I understand there is no benefit to running a 1:1 like the op suggests/talks about.. The ratio is the same 1:4, etc, it all scales and = the same thing.
a b K Overclocking
December 14, 2009 3:25:02 PM

I just noticed you have black edition cpu, if I where you I would not even bother with the frequency setting, just raise the multiplier since its unlocked for you cpu.

I have had my frequency up to 250, you just have to scale some other things back is all.

Paul
February 3, 2010 9:47:53 AM

I just have a theory question here.

If I set FSB (reference clock) on my MB to 400 and then changed my NB multiplyer to 5 (from 10) so it still get 2000. And change my ram speed from 400 to 200, and my HT multiplyer from x4 to 2x. then finally lowered my processor multiplyer from 14 to 7.

(bascically double FSB and half all multipliers) would my computer be just be back at stock (no OC). I think this is the way that it works, I am just not sure if the FSB (reference clock) actually does anything but act as a mutliplyer?
a b à CPUs
a b } Memory
a b K Overclocking
February 4, 2010 5:47:28 PM

Quote:
But in any case, my question is still valid -,How can you NOT bottleneck your system if you dont run your fsb/memory controller at 1:1 frequency with your ram.


Your RAM is the fastest piece of hardware, you are not bottlenecking anything by NOT having your ratio at 1:1 . I change my ratio from 1:2 to 1:4 and I cannot tell the difference. So dont worry about your ratio, just make sure your timings/voltage and frequency are correct.

a b à CPUs
a b } Memory
a b K Overclocking
February 4, 2010 6:01:37 PM

thegreat1 said:
from what ive come to understand on AMD systems you cant really touch the Reference frequncy. Youre stuck at 200mhz becuase the whole system including the NB runs at that. If you touch it a bit the system will probably go wonkie. There is probably a TINY bit of room to up the frequency, but not much.. maybe 210-215, and youd be at the upper edge of stability. Everything gets over clocked when you do this - the entire system, so expect more heat, less stability, etc. And from what I understand there is no benefit to running a 1:1 like the op suggests/talks about.. The ratio is the same 1:4, etc, it all scales and = the same thing.


False, I can run my FSB at 260 and still be able to achieve 3.9Ghz with timings of 6-6-6-18. I also have a buddy here that runs his FSB at 345 on an MSI 790FX. It all comes down to lowering your multiplier and making sure you have the correct voltages. The HT link also should be adjusted according to the CPU clock.


February 5, 2010 4:46:12 PM

200 mhz IS a 1:1, it is a quad core... each core = 200. 200x4=800...
So if you raise this to 250, you are at 1000, etc. As for the entire board getting overclocked, that is news to me. (I'm a noob though.)
My clocker is a clunker. :) 
MSI k8n-neo v2.0
AMD Athlon 64 3000+ @2.4 ghz (240 fsb, 3 HT freq)
DDR400 ram @ 2-2-2-6, 133 mhz (wintec ampo)
-stock was 200 mhz but 6-6-6-18
The chip is stock at 2.0 ghz, so 2.4 is a 20-25% gain. The stock HT is at 4 though. 200x4=800 HT. (Idles at 38 C) 2.0 ghz
240x3=720 HT. (Idles at 31 C) 2.4 ghz
!