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sync / async timings when using core 2 duo?

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#1
hosko

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Is it better to keep the memory in sync with the fsb on a core 2 dou system? My only experience with a fsb is with the amd k7 architecture as the k8 architecture is different. From what i can understand k7 is the same as core 2 duo except that intel quad pump instead of double pump there fsb. With k7 it was best to keep your memory and fsb at 1:1 (in sync). By this I mean a fsb running at 400mhz (200mhz double pumped) should be paired with ddr400 (PC3200) memory keeping fsb:memory ratio 1:1. My question is whether a e6300 with a 1066mhz fsb needs to be paired with either 1 dimm of 1066 mhz or 2 dimms at 533mhz in dual channel so that the memory and fsb run 1:1. What happens when you put in 1 dimm of ddr2 800 memory which gives async ratio of 4:3 (1066:800) or 2 dimms of ddr2 800 memory in dual channel which gives a async ratio of 2:3 (1066:1600). Are there benefit in choosing faster memory if it is not going to run 1:1 with the fsb? Should I choose 2 dimms of ddr2 533 or 2 dimms of ddr2 800 for my new core 2 duo build for max performance/value for money?

#2
Komet

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Ok, uhm, gonna break this one down.
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
Is it better to keep the memory in sync with the fsb on a core 2 dou system?
Nah, it doesn't really matter and you'll end up having to run a divider anyhow.
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
My only experience with a fsb is with the amd k7 architecture as the k8 architecture is different. From what i can understand k7 is the same as core 2 duo except that intel quad pump instead of double pump there fsb.
<_<, uhm, effective dual data rate doesn't really...mean... it's going that fast...
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
With k7 it was best to keep your memory and fsb at 1:1 (in sync). By this I mean a fsb running at 400mhz (200mhz double pumped) should be paired with ddr400 (PC3200) memory keeping fsb:memory ratio 1:1.
Well, as long as that's what your mobo supported. Or in this case your CPU, so I should say what your memory controller supported. Speeding up the ram only means data spends less time in transit between there and a register...
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
My question is whether a e6300 with a 1066mhz fsb needs to be paired with either 1 dimm of 1066 mhz or 2 dimms at 533mhz in dual channel so that the memory and fsb run 1:1.
Now, what the fuck. Ok, uhm, it doesn't work like that. Single channel doesn't mean it's going half as fast, it means it can only use one 64bit data channel instead of two...speed doesn't have anything to do with it. Here, read this.
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
What happens when you put in 1 dimm of ddr2 800 memory which gives async ratio of 4:3 (1066:800) or 2 dimms of ddr2 800 memory in dual channel which gives a async ratio of 2:3 (1066:1600).
As above, dual channel doesn't work like that. Your sync ratio isn't dependent on the number of dimms populated. DDR2 800 is the standard spec for C2D and won't cause the system to be bottlenecked at stock speeds (1066 on the CPU goes through the 4:3 divider to give the ram 800).
QUOTE (hosko @ Feb 21 2007, 05:08 PM) <{POST_SNAPBACK}>
Are there benefit in choosing faster memory if it is not going to run 1:1 with the fsb? Should I choose 2 dimms of ddr2 533 or 2 dimms of ddr2 800 for my new core 2 duo build for max performance/value for money?
As above, you should definitely choose DDR2 800, because it's the standard spec for DDR2 on C2D systems. DDR2 533 is considered pretty much slow as shit in comparison. If you're into overclocking, or want to try and achieve 1:1 on the ram at stock speeds, buy a good DDR2 kit with Micron D9GMH chips, and it should be able to hit 1066, or pretty damn close.

#3
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Ok, having the 1:1 divider is nice but not necessary. Just use DDR2 800 on your C2D and all the little pixies will be happy

Have you tried turning it off and on again?
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#4
hosko

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It seems I have a fairly messed up understanding. Below I've summarized my understanding in a few statements. Please correct me where I am wrong!

1. The e6??? series of cards have a 1066mhz fsb or 266 base clock quad pumped.

2. The memory clock speed is generated by passing the fsb clock through a divider.

3. When you use the 1:1 divider your memory is in sync with your fsb. Thus to use a 1:1 divider with a e6??? proc you need memory that can cope at 1066mhz which is what ddr2 1066 memory is capable of doing.

4. Memory derives the clock that it runs off from the fsb. If im using a e6300 paired with memory badged at ddr2 800 I would need to select the 4:3 divider as a 4:3 divider ramps down the fsb at 1066 mhz to 800 mhz (NB i understand that the divider doesnt actually change the fsb but generates the clock at which the memory is going to run off). If I didn't select the 4:3 divider but instead the 1:1 divider my memory would attempt to operate at 1066 mhz which would most likely not work.

5. ddr2 533 memory in dual channel can generate enough bandwidth to fill the core 2 duo fsb.

Bandwidth of the fsb: 1066 000 000 hz * 64 bit wide bus = 68224000000 bit/s

68224000000/(8 * 1000000) = 8528 mb/s

Bandwidth of ddr2 533 memory (in dual channel): 533 000 000 hz * 2 by 64 bit wide bus (in dual channel) = 68224000000 bit/s

68224000000/(8 * 1000000) = 8528 mb/s

Since ddr2 533 memory in dual channel can completely fill the fsb why get memory any faster than ddr2 533?

Thats all for now. Thanks

#5
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I wrote this and then I fucked it up. I'm much more comfortable with the way that AMD used to do the whole deal, the strange frequencies fuck me up. It's fixed now.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
1. The e6??? series of cards have a 1066mhz fsb or 266 base clock quad pumped.
The front side bus operates at 266mhz and is then multiplied by whatever multiplier your cpu will allow. The overall system bus speed is 1066. Not really sure where the 1066 is coming into play, n00b m4573r can probably explain it better than me.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
2. The memory clock speed is generated by passing the fsb clock through a divider.
Right. So 266 passed into FSB:DRAM (2:3) = 400 = DDR2 800.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
3. When you use the 1:1 divider your memory is in sync with your fsb. Thus to use a 1:1 divider with a e6??? proc you need memory that can cope at 1066mhz which is what ddr2 1066 memory is capable of doing.
Your memory isn't in sync because it's still running faster than the fsb. Ram specced to run at DDR2 1066 (533mhz) will run at 1:1 if your fsb was 533, but if your fsb was 266 you'd need 2:1.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
4. Memory derives the clock that it runs off from the fsb. If im using a e6300 paired with memory badged at ddr2 800 I would need to select the 4:3 divider as a 4:3 divider ramps down the fsb at 1066 mhz to 800 mhz (NB i understand that the divider doesnt actually change the fsb but generates the clock at which the memory is going to run off).
The 4:3 divider would make your ram run at 200mhz. 266 * 3 / 4 = 200 = DDR2 400.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
If I didn't select the 4:3 divider but instead the 1:1 divider my memory would attempt to operate at 1066 mhz which would most likely not work.
If you selected 1:1, your ram would operate at 266mhz, or DDR2 533.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
5. ddr2 533 memory in dual channel can generate enough bandwidth to fill the core 2 duo fsb.
Uhm, no not really. It just happens to run at 1:1.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
Bandwidth of the fsb: 1066 000 000 hz * 64 bit wide bus = 68224000000 bit/s

68224000000/(8 * 1000000) = 8528 mb/s

Bandwidth of ddr2 533 memory (in dual channel): 533 000 000 hz * 2 by 64 bit wide bus (in dual channel) = 68224000000 bit/s

68224000000/(8 * 1000000) = 8528 mb/s
Yeah, uhm, that's not how it works at all.
QUOTE (hosko @ Feb 21 2007, 08:58 PM) <{POST_SNAPBACK}>
Since ddr2 533 memory in dual channel can completely fill the fsb why get memory any faster than ddr2 533?
Dual channel doesn't have that kind of effect. It doubles the lanes, not the speed of the cars. The cars can go faster because there's more room to speed, but they won't go twice as fast.

#6
hosko

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Thanks Komet that mostly clears it up apart from the calculations. I forgot to take quad pumping and double data rate into consideration. 1066mhz is the effective clock rate. In actual fact the clock is only going at 266 mhz, however every clock cycle it is completing 4 data transfers. What intel mean by an fsb of 1066 is that if I were to only complete 1 data transfer instead of 4 per clock cycle the equivalent bus mhz would have to be 1066mhz ie 266 * 4. I was using the effective clock rate instead of the actual clock rate.

Yes I agree with your memory dividers. I don't agree that my calculations are wrong. (maybe i've got the bus width wrong).

QUOTE
It doubles the lanes, not the speed of the cars. The cars can go faster because there's more room to speed, but they won't go twice as fast.
Keeping with the dual channel highway analogy. If you double the lanes that doubles the amount of cars that can pass per data transfer. If cars are data and you double the amount of data that can fit through each data transfer u are doubling the peak bandwidth.

The previous link u provided supports this:

QUOTE
The dual channel configuration alleviates the problem by doubling the amount of available memory bandwidth.


#7
Komet

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Oh, well, maybe that's right but I've never tried not using dual channel, so yeah.

#8
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posting in epic thread.
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#9
SideswipeZulu

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QUOTE (stabhappy @ Feb 22 2007, 01:35 AM) <{POST_SNAPBACK}>
posting in epic thread.

What, Komet getting 1up'd? pp_smiley4.gif
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#10
Komet

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999/1000 ain't bad.

If you take for example I've had about 400 utter shit posts, that leaves me being wrong about 8 times in the past year and 3 months.

#11
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QUOTE (Komet @ Feb 22 2007, 02:00 AM) <{POST_SNAPBACK}>
999/1000 ain't bad.

If you take for example I've had about 400 utter shit posts, that leaves me being wrong about 8 times in the past year and 3 months.

Your ego fits through doorways? That's enough to impress. ^_^
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#12
Komet

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QUOTE (SideswipeZulu @ Feb 22 2007, 12:08 AM) <{POST_SNAPBACK}>
You're ego fits through doorways? That's enough to impress. ^_^
It doesn't, actually.

And you spelled your wrong.

#13
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QUOTE (Komet @ Feb 22 2007, 02:23 AM) <{POST_SNAPBACK}>
It doesn't, actually.

And you spelled your wrong.

Holy nub-i-fied! Corrected.
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#14
7h3 n00b m4573r

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QUOTE (hosko @ Feb 21 2007, 11:58 PM) <{POST_SNAPBACK}>
1. The e6??? series of cards have a 1066mhz fsb or 266 base clock quad pumped.

Correct
QUOTE (hosko @ Feb 21 2007, 11:58 PM) <{POST_SNAPBACK}>
2. The memory clock speed is generated by passing the fsb clock through a divider.

Wrong, its obtained by passing whats called the host frequency through a divider. Your FSB is 1066MHz, your host frequency is 266MHz.
All components in the computer run at certain clock speeds, these need a clock generator. The host frequency is the frequency of a clock generator on your motherboard. Most of the components plugged into your motherboard pass the host frequency through a divider of some sort.

QUOTE (hosko @ Feb 21 2007, 11:58 PM) <{POST_SNAPBACK}>
3. When you use the 1:1 divider your memory is in sync with your fsb. Thus to use a 1:1 divider with a e6??? proc you need memory that can cope at 1066mhz which is what ddr2 1066 memory is capable of doing.


Sorry but completely wrong. The divider of 1:1 refers to your host frequency not your FSB. So 1:1 with your default 266Mhz FSB = 266MHz RAM speed. Due to being DDR though the RAM does its data sending thing twice per clock cycle instead of once so you double it ie 266x2=533 and thus you have DDR2 533MHz so at 1:1 core a core2duo e6xxx CPU you have DDR2 533 RAM.

QUOTE (hosko @ Feb 21 2007, 11:58 PM) <{POST_SNAPBACK}>
4. Memory derives the clock that it runs off from the fsb. If im using a e6300 paired with memory badged at ddr2 800 I would need to select the 4:3 divider as a 4:3 divider ramps down the fsb at 1066 mhz to 800 mhz (NB i understand that the divider doesnt actually change the fsb but generates the clock at which the memory is going to run off). If I didn't select the 4:3 divider but instead the 1:1 divider my memory would attempt to operate at 1066 mhz which would most likely not work.

Yes except the 1:1 would be 533MHz now 1066MHz icon_wink.gif
To get DDR2 1066MHz you'd either need a 2:1 divider or an overclock

QUOTE (hosko @ Feb 21 2007, 11:58 PM) <{POST_SNAPBACK}>
Since ddr2 533 memory in dual channel can completely fill the fsb why get memory any faster than ddr2 533?

Not really as you obtain higher benchmarks when you have higher speed memory, sure if you look at the bandwidth of just the memory 128bit (dual channel) at 533MHz and the FSB of 64bit at 1066MHz they are in theory the same. However multiple things use the FSB and the RAM simultaneously, like the GPU or the HDD might be buffering something into RAM and latency also comes into play.

Have you tried turning it off and on again?
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#15
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Okay! Here is what I've come to understand about this (minus the whole system Bus 4:3 DRAM thing);

1. DDR2-800 RAM is the standard because with the e6600's FSB of 266 MHz, the divider is 2:3 (266*(3/2) = 400MHz, or DDR2-800)
2. If I change the divider to 1:1 without changing the FSB, the RAM operates at DDR2-533, which is slow as shit.
3. If I want 1:1 and DDR2-800, I have to increase the FSB of the e6600 to 400MHz, which makes a clock speed of 3.6GHz (glee!).

Now, I think that "quad pumped" means that 1066MHz/4 = 266.5, which is more or less the stock FSB of the CPU (2400/9 = 266.667).

Note that I'm not up to speed on proper terminology, but I believe my simple math is sound.

#16
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You're pretty much correct. I've got a 8x processor, so I'd need to take my FSB to 400ish also to get the ddr800 @ 1:1. However, I plan on going higher than 2.8ghz so I'm experiment with more exotic ram dividers.
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