Question about asynchronous memory / CPU FSB

Arghuin · May 31, 2002

I have an Abit KX7-333 and I know that on the AXP systems coupled with DDR 2700 mem, you get 133 mhz = CPU FSB and 166 mhz = mem fsb.....

My question is, what is the dynamic relationship between the two? (ie how does the mem fsb change in relation to the CPU fsb)?

For example, if I up my CPU FSB to say 135-138 MHz, will I still be able to run my mem asynchronously? (what a word

) i.e mem fsb = 135+33 = 168?

Or will I have to change it to synchronous mode in the BIOS? :eh?:

Again thx for your help

PS: been through the guides, but they seem to deal more with Athlon-based systems and sort of overclocking 'principles' and 'examples'...unless if I missed something (which I usually do

)

XiveX · May 31, 2002

I'm curious too...bump. Is it that you can set the memory and FSB speeds independently of each other if you do NOT use the 133/166 spec, or how does that work?

XiveX

Are there any mobo's out where you can set FSB (in 1 Mhz increments) and Memory speed INDEPENDTLY OF each other? This newer asus board seems like it is attempting to do that, but with only 133/166 or 100/133 to choose from....its not quite there yet..

Arghuin · May 31, 2002

That's exactly my question

Thing is, you have the BIOS option 'by SPD' (Serial Presence Detect), or atleast my Abit KX7-333 has it, which allows the BIOS to automatically set the memory's FSB by detecting what type of memory you have (in my case Smasung DDR 2700, thus mem fsb = 166)

HOWEVER in KT266 /333 mobos commonly mem fsb = cpu fsb + 33

SO....to repeat my question: if one changes the fsb to say 138 then mem fsb = 138 + 33 = 173 or the SPD setting in the BIOS no longer holds, in which case one would have the following options:
-set frequency manually (would the system allow for a mem fsb of 166 even when the cpu is not at 133?)
-set mem to be at the same fsb as the CPU (extremely useful if you have unlocked the cpu and bumped the fsb up to 166

)

So...errm...any overclockers with experience on independence as XiveX put it feel free to join us

{PMS}fishy · Jun 1, 2002

What happens is that you have different dividors that you can sellect. I am not dirrectly framiler with these two boards. However on my Ait ST-6 you can select different dividors that make the PCI and Memory clocks different than the fronside bus. I believe that the KT333 chipset does this aswell with a 4/5 memory divisor. Making the cpu FSB be 133 and the memory bus to 166. So you are partley correct. They do not move 1 to 1 but rather 4 to 5. See if this example helps. CPU:MEM = 133:166 = 150:188. Take your CPU FSB and divide that by 4 then multiply that numer by 5 to get what your memory is running at. (that is only the case for 4:5 divisors. There are also different ones.)

Arghuin · Jun 1, 2002

Cheers

So the mem fsb is on cpu fsb+33 then

Question is, when you alter the cpu fsb in the bios and you have the mem as 'SPD detect' (i.e auto set to 166) will that cause problems?

Or should one simply set the mem fsb manually?

To what tho? :eh?:

{PMS}fishy · Jun 1, 2002

Arghuin said:
Cheers

So the mem fsb is on cpu fsb+33 then

No it is not strickly +33 as you can see in my example when the cpu is at 150 the memory is at 188 which is a 38mhz difference. It is figured by the ratio 4CPU=5FSB or 4/5

Arghuin · Jun 1, 2002

True.....(mental note: visit the oc forum after you've slept properly

)

Thing is, are these divisors auto then? Because for my KX7-333, the only fsb settings that seem to be available for the memory (DRAM Clock) are 100, 133 and by SPD...so what does that mean?

If the memory is set to SPD, then it will 'stay' at 166 regardless of the cpu's fsb? :eh?:

Again thx for your help

Arghuin · Jun 2, 2002

Also one more thing....

I have manually set the mem fsb in the BIOS to 166...so...the BIOS reports it as 166, but Sandra reports it as 134 (which is actually my current cpu fsb)...which one of them is at fault? :eh?:

Is there any other program/way to verify what the actual settings are and also to see what my AGP/PCI frequencies are at the moment?

Sonny · Jun 2, 2002

What does WCPUID say? Could you show what exactly you have in SOFT MENU III & please make sure not to simplify anything :beer:

Arghuin · Jun 2, 2002

Sonny to the rescue

OK m8, WCPUID says system bus = 133.90

Softmenu III settings:

All voltages default
Processor set to user define as an AXP 1600+ so...multiplier 10.5, fsb = 133
Speed error hold disabled
Enhance for benchmark enabled<----abit's way of pinching up the fsb methinks
CPU fast command decode set to Ultra
FSB:AGP

CI dividers set up as 4:2:1

Sandra says mem speed at 2x134 with a multi of 1, agp speed 4x68 and PCI bus speed 34.

Also run wpcredit and in register 69 bit 6 it shows
DRAM faster than CPU enabled (1) with DRAM+33= CPU :eh?:

On the other hand, same register bit 7:
CPU faster than DRAM is disabled, with options 0: DRAM = CPU and 1: CPU + 33 = DRAM.

Sonny · Jun 2, 2002

Well your running Asychronously with your CPU at 133MHz/266FSB & your Memory is running at 2 X 166MHz = DDR333. Your Divisors are set to 4(PCI):2(AGP):1(CPU@4/5) I think. Have you unlocked that chip yet? Running Asychn defeats the purpose of the KT333 chipset. I am not familiar with your PCR File since I do not like the KT333 but it looks like all it saying is that your in Asychn in it's own confusing way. Try running 5:2.5:1 at 8.5 X 166 & see if you like it better than what you have now. Also do a back to back test of 8.5 X 166 vs 8.5 X 164 with 3DMark2001SE & show us which scores higher.

Arghuin · Jun 2, 2002

Cheers for the help

I haven't unlocked the chip yet (probably won't for an extra couple of months)

As for the .PCR file, I am using the KT266 one since people at the viahardware forums siad that the registers were essentially the same...

Also the 5:2.5:1 divisor that you mentioned does not exist on the KX7 mobo

Sonny · Jun 2, 2002

Maybe that's why you have funny registers but I still need to get more experience with the KT266A PCR Files. I wasnt sure about the 5:2.5:1, just trying to look for the right divisor, or you have to set the memory to run sychronously in ADVANCED CHIPSET FEATURES to enable it. While your at it list down what you have there.

Arghuin · Jun 2, 2002

I currently have the processor set at 134 fsb + enhance for benchmark is on, which adds a 0.5 to the fsb and rounds it up = 135 fsb

For the memory under advanced chipset features, it says fsb = 133

and mem fsb = 166...still in Sandra tho I get that mem fsb = cpu fsb

Other settings (again for memory):
DRAM Clock 166
DRAM Timing Manual
Cas latency 2
Bank Interleave 4
Precharge to active 2T
Active to precharge 5T
Active to CMD 2T
DDR DQS Input delay Auto
MD Drive strength
MD drive strength both these set to auto
DRAM Access 2T
DRAM Queue Depth 4 level
DRAM Command Rate 2T (I should prolly set this to 1T but I'm worried about mem stability)
DClock Feedback Delay 0 ps

These are the settings....

Arghuin · Jun 2, 2002

D'OH

Taken from Sisoftware's Sandra site:

VIA KT333 Chipset: Detected as KT266/A since it has the same ID. Also, 2x 166MHz memory speed detected incorrectly as 2x 133MHz, the 133/166 multiplier is not supported. (next version will fix)

So much for all these mem benchmarks and hassle then people

Sonny · Jun 2, 2002

I did some reading & your suppose to have a 5:2:1 in SOFT MENU III so try it if you think you can go 10.5 X 166, then set your DRAM CLOCK to 166 & make sure to MAX OUT

your VCore. Well you can IF you have good cooling. Let me remind you again. ONLY IF YOU HAVE GOOD COOLING!!!!!

If not set it at 4:2:1, FSB = 133MHz & your DRAM CLOCK to 133. Hopefuly that will force it to run Sychronously then you can raise the FSB using the + feature in SM III.

Arghuin · Jun 2, 2002

True I _do_ have the 5:2:1 but my cooling is not _that_ good

to take it all the way up to 166....so now (until I unlock it at some point

) I have it at 4:2:1 with fsb ~135/140 and mem at 166

Awaiting newer Sandra revision then

Sonny · Jun 2, 2002

I wanted to see you hit 1743MHz!!!!! Ahh well better safe than sorry :burn:

You could just try right? I mean it will just lockup if it's too hot right? What harm could that do? Don't you have the urge to make that sucker beg you to stop pushing it? C'mon man do it for the love of BURNT CPU smell.....

Arghuin · Jun 2, 2002

No worries

I'll do it but not yet....need a better fan and stronger PSU first (not to mention that I have to buy a new gfx card

Thing is I _do_ have PC Health enabled in the BIOS so...if the CPU exceeds a certain temperature the system should automatically shut down right?

Sonny · Jun 2, 2002

Hope you get the right parts soon :beer:

Question about asynchronous memory / CPU FSB

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