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FSB, Memory Speed, Core speed... Lemme get this straight.

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June 1, 2007 6:11:58 AM

Okay, let's use a Q6600 for an example. Can someone help me fill in the blanks?

Core clock speed = 2.40, so that means internal multiplier = 9
No confusion here.

Base FSB = 266Mhz x QDR = Effective FSB = 1064 right?
Exactly what does the CPU communicate with at this speed?

Memory speed = 266 x DDR = 533?
If that was the case, does that mean the new 6X50s are going to need DDR2-667Mhz memory? Or am I confused here? What uses the DDR2-800? I can see it in a price list, but no CPU I can see uses it. Is that a bit of a gimmick, or for overclockers?

If I got DDR2-800, would it "underclock" back to 533 when paired with a Q6600? Are there any disadvantages? (IE, slower latency?)

On the flip side, does that mean if I overclock my FSB to 400 (assuming it will survive to that speed, which I know is unlikely), that the memory is not overclocked and running at the correct speed? Or if I could overclock it to say 333Mhz, would the RAM speed match without instability?

On yet another thought, I think I've seen motherboards where you can change the "ratios" between different buses. Is it possible for example, to keep the CPU FSB at 266, but pump the memory FSB to 400 in order to run DDR2-800 with a Q6600 without overclocking?

I've been out of the hardware game way too long. A catch up lesson would be very much appreciated. Thanks.
June 1, 2007 6:35:51 AM

I'll... try to answer correctly.

Quote:
Base FSB = 266Mhz x QDR = Effective FSB = 1064 right?
Exactly what does the CPU communicate with at this speed?


That would be to the ram, quad pumped.

Quote:
Memory speed = 266 x DDR = 533?
If that was the case, does that mean the new 6X50s are going to need DDR2-667Mhz memory? Or am I confused here? What uses the DDR2-800? I can see it in a price list, but no CPU I can see uses it. Is that a bit of a gimmick, or for overclockers?

If I got DDR2-800, would it "underclock" back to 533 when paired with a Q6600? Are there any disadvantages? (IE, slower latency?)


Since the E6X50's are 1333 FSB rated, yes the base speed for ram is 333 x 4 (DDR2 667).

Yes, DDR2 800 would be running slower or underclocked. I guess you could think of it as a gimmick (if you don't over clock), but yes DDR2 800 can be used for over clocking. But then DDR2 667 can reach DDR2 800 speeds, but DDR2 800 can get close to DDR 1066 speeds.

Quote:
On the flip side, does that mean if I overclock my FSB to 400 (assuming it will survive to that speed, which I know is unlikely), that the memory is not overclocked and running at the correct speed? Or if I could overclock it to say 333Mhz, would the RAM speed match without instability?


DDR2 800 advertised speed is 400. So running the Q6600 at that speed would force it to run 400 x 9 = 3600 mhz or 3.6 ghz. Running it at DDR2 667 advertised speed would force it to run 333 x 9 = 2997mhz or 3 ghz. But to get them stable is the other trick with voltage settings.

So your FSB rated at 800 speed is 1600 mhz. At 667 speed, your rated FSB is 1333mhz.

Quote:
On yet another thought, I think I've seen motherboards where you can change the "ratios" between different buses. Is it possible for example, to keep the CPU FSB at 266, but pump the memory FSB to 400 in order to run DDR2-800 with a Q6600 without overclocking?


Ummm... No. When you run the Q6600 for a 1:1 ratio, you need to run it at 533 speeds. If you run it at a 1:1 ratio of the advertise speeds of DDR2 667 or 800, it will over clock the CPU.
June 1, 2007 6:48:44 AM

Quote:

On yet another thought, I think I've seen motherboards where you can change the "ratios" between different buses. Is it possible for example, to keep the CPU FSB at 266, but pump the memory FSB to 400 in order to run DDR2-800 with a Q6600 without overclocking?


Ummm... No. When you run the Q6600 for a 1:1 ratio, you need to run it at 533 speeds. If you run it at a 1:1 ratio of the advertise speeds of DDR2 667 or 800, it will over clock the CPU.

Thanks Grimmy, fantastic, short and very clear answers.

I just checked, and the settings were only for FSB/AGP/PCI ratios, not for FSB to memory speed ratios, so it wasn't even relevant. I must have been dreaming :oops: 

I also did some research and I think they said DDR2-800 can be used in single channel configurations instead of dual channel DDR2-400. Know anything about that?

EDIT: Never mind - it all makes sense to me now. If the FSB is 800, then clearly, a single channel of DDR2-400 can't keep up, and dual channel is required... but having the ridiculously fast DDR2-800, you could have a single stick of RAM and still keep all the 200xQDR CPUs happy. This is starting to make more sense!
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June 1, 2007 6:55:46 AM

Quote:
Okay, let's use a Q6600 for an example. Can someone help me fill in the blanks?

Core clock speed = 2.40, so that means internal multiplier = 9
No confusion here.

Base FSB = 266Mhz x QDR = Effective FSB = 1064 right?
Exactly what does the CPU communicate with at this speed?

Memory speed = 266 x DDR = 533?
If that was the case, does that mean the new 6X50s are going to need DDR2-667Mhz memory? Or am I confused here? What uses the DDR2-800? I can see it in a price list, but no CPU I can see uses it. Is that a bit of a gimmick, or for overclockers?

If I got DDR2-800, would it "underclock" back to 533 when paired with a Q6600? Are there any disadvantages? (IE, slower latency?)

On the flip side, does that mean if I overclock my FSB to 400 (assuming it will survive to that speed, which I know is unlikely), that the memory is not overclocked and running at the correct speed? Or if I could overclock it to say 333Mhz, would the RAM speed match without instability?

On yet another thought, I think I've seen motherboards where you can change the "ratios" between different buses. Is it possible for example, to keep the CPU FSB at 266, but pump the memory FSB to 400 in order to run DDR2-800 with a Q6600 without overclocking?

I've been out of the hardware game way too long. A catch up lesson would be very much appreciated. Thanks.
Yes, you can run the memory asynchronously(faster or slower than FSB),without touching CPU frequency....ex. 266FSB/800RAM(2:3). You can also run it at 266/667(4:5), and yes ..there is a latency penalty for running out of sync....therefore running @ 4:5(667) is often slower than 1:1...but jumping up to 800MHz(2:3)...the RAM speed is so fast that it effectively negates the latency penalty....and can increase performance. DDR2-667 also allows for an overclock to 333FSB, while still running synchronously, as DDR2-800 offers the same benefit, but @ 400FSB. Another possible benefit to the higher rated DIMM's(ie.DDR2-800), is that many times they can run at the slower speed(533/667) with tightened timings. :) 
June 1, 2007 6:57:30 AM

Well, at stock speeds the video is on a different bus speed, so in OC the system, you want to lock it down. Mainly all new MB will have PCI-E at 100mhz, in relation to the AGP's 66mhz, if I remember right. :oops:  . o O (getting weally late here)

DDR2 800 or DDR400 can be run in single or dual channel, depending on the chipset, as well as memory modules.

So in order to run dual channel, you need at least 2 sticks. So when you look at a system board, with 4 slots, 2 of those slots will be of separte channels:

One Channel
Dimm 1
Dimm 2

Other Channel
Dimm 3
Dimm 4

So dimms 1 and 3 make a dual channel. If just Dimm 1 is filled, its single channel as well as having both 1 & 2 filled still single channel.

Hope that makes sense.

Edit:

wow, some responds came up... I'll let you gents take over. Night! :D 
a c 87 à CPUs
a b } Memory
June 1, 2007 7:08:21 AM

Quote:

Base FSB = 266Mhz x QDR = Effective FSB = 1064 right?
Exactly what does the CPU communicate with at this speed?


Grimmy is wrong. The CPU uses the FSB to talk to the northbridge, not the ram. This is one reason why the Athlon arch is considered suppior to Intels, as they don't need to talk to the northbridge to get to the memory.

Quote:
If I got DDR2-800, would it "underclock" back to 533 when paired with a Q6600? Are there any disadvantages? (IE, slower latency?)


If you left the bios settings at stock, it would underclock. There aren't any real disadvantages, other then spending more money then you needed. You could probably tighten the timings a lot. If the ram is rated CL5 at 800MHz, it might be able to do CL3 at 533MHz.

Quote:
On the flip side, does that mean if I overclock my FSB to 400 (assuming it will survive to that speed, which I know is unlikely), that the memory is not overclocked and running at the correct speed? Or if I could overclock it to say 333Mhz, would the RAM speed match without instability?


This is actually very doable. Some people can get to 500MHz depending on chip/motherboard. If you leave the FSB:RAM ratio at 1:1 and overclock the FSB to 400, then you are properly using your DDR2-800 ram.

Quote:
On yet another thought, I think I've seen motherboards where you can change the "ratios" between different buses. Is it possible for example, to keep the CPU FSB at 266, but pump the memory FSB to 400 in order to run DDR2-800 with a Q6600 without overclocking?


(266MHz * 3)/ 2 = 400MHz DDR rate of 800MHz. This means that the ratio you'd want to use is 3:2.

Quote:
I've been out of the hardware game way too long. A catch up lesson would be very much appreciated. Thanks.


No problem. Keep reading and asking questions.[/quote]
June 1, 2007 7:09:42 AM

Quote:
Yes, you can run the memory asynchronously(faster or slower than FSB),without touching CPU frequency....ex. 266FSB/800RAM(2:3). You can also run it at 266/667(4:5), and yes ..there is a latency penalty for running out of sync....therefore running @ 4:5(667) is often slower than 1:1...


I would guess that the latency is caused by a wasted cycle approach translating the clock speeds (I.E. in a 4:5 ratio every 5th cycle, the RAM just doesn't bother to read, knowing the CPU won't have time to take it?)

Does that mean a more even ratio, say 266/1066 (2:4) wouldn't have any wasted cycles?
June 1, 2007 7:13:15 AM

Quote:
Yes, you can run the memory asynchronously(faster or slower than FSB),without touching CPU frequency....ex. 266FSB/800RAM(2:3). You can also run it at 266/667(4:5), and yes ..there is a latency penalty for running out of sync....therefore running @ 4:5(667) is often slower than 1:1...


I would guess that the latency is caused by a wasted cycle approach translating the clock speeds (I.E. in a 4:5 ratio every 5th cycle, the RAM just doesn't bother to read, knowing the CPU won't have time to take it?)

Does that mean a more even ratio, say 266/1066 (2:4) wouldn't have any wasted cycles?I'm not positive, but i don't think that odd/even #'s plays into it. :?
June 1, 2007 7:14:17 AM

You guys are fantastic!

Thanks for the quick responses. I think I'm starting to catch up already!
a c 87 à CPUs
a b } Memory
June 1, 2007 7:44:19 AM

Have you never read a block diagram of a motherboard?

Block diagram of a 650i.

Where do the lines point to for the CPU? Does it point to the ram? Video card? SATA ports? Do they lines (which is the FSB) point to anything OTHER then the northbridge?

Block diagram for an AM2 motherboard.

I couldn't find one that showed the memory access lines. Notice that there aren't any between the RAM and the northbridge. Remember that AMD has an IMC (integraded memory controller) so memory requests go directly from the CPU to the ram. Superior was the wrong word, elegent is more appropriate...
a c 87 à CPUs
a b } Memory
June 1, 2007 7:51:30 AM

The memory controller, which is a part of the traditional northbridge, is on the CPU. I don't care if you call it a northbridge or a SPP, they (almost) do the same thing. (the SPP doesn't need a memory controller...)

Remember that AMDs don't use a FSB, Intel does. As such, the Intel block diagram is more "important". It clearly shows that the CPU does NOT communicate with the other devices. "northbridge" only. I don't know why your links claim that the FSB allows the CPU to talk to the RAM or other devices, but I assure you they are wrong.

The Intel CPU does talk to the other devices, buy only by extension of the Northbridge.

EDIT: LOL, I just read part of your wiki link. (I haven't edited it yet...)

Quote:
Setting a FSB speed is related directly to the speed grade of memory that a system must use. The memory bus connects the northbridge and RAM, just as the front side bus connects the CPU and northbridge.

It seems that someone changed the "header" part of it, while not changing the lower part. (or vis versa...)
June 1, 2007 7:57:52 AM

Actually before I really literally hit the sack...

I was just answering the question at its face value.

He asked what does it talk to at that speed. Okay, the northbridge does have the memory controller, but it talks to the RAM at that speed.

I don't see the CPU talking to anything else at 200-266-333-400-500-533mhz quad pumped. (Geee.. what if the CPU did talk to the video card at the same speed?)

So technically, you are correct, but I'm not totally wrong. :cry: 

:oops:  . o O (hate it when insomnia kicks in)

Edit:

And why did you bring the AM2 into this discussion?
a c 87 à CPUs
a b } Memory
June 1, 2007 8:10:25 AM

Quote:
but it talks to the RAM at that speed.


This is correct, depending on what "it" is.

Actually, I can't believe I missed this.

Quote:
That would be to the ram, quad pumped.


The base frequency is quad pumped to give you the effective FSB. The RAM data rate is only double. Again, read the block diagram to see who talks to what. The FSB is the link between the CPU and the "northbridge". The northbridge has various other buses that it uses to talk to different things. I only brought AM2 into this to try to show how AMD CPUs are different from Intels, but that didn't go so well. I can't find a block diagram that shows the memory access. It should be attached to the CPU at the top, as thats where the memory controller is.
June 1, 2007 8:23:04 AM

I understand the diagram well enough... I think (has one eye open :lol: )

I was just trying to make my answers quick and easy to understand.

Sorry that the AM2 description didn't go so well. Just kinda thought it was going to become some kind of flame war, from the choice of words.

Elegant is better word for describing it, but everything does have its pros and cons.

I can't believe it took me 5 mins to type all that...

Nite.
a c 87 à CPUs
a b } Memory
June 1, 2007 8:28:35 AM

I by no means ment to imply that AMDs K8 arch is better then C2D. Intel has done a great job at keeping something as old as the FSB, etc going. Elegant is a much better word. Vern seemed to be implying that I might be wrong, but after reading his links, I'm not convinced. Hopefully he'll be able to tell me what I'm missing.

Are you drinking regular SoCo, or the 100proof stuff that I do shots of? I'm only drinking lemonade right now, but its laced with Vodka and Everclear....
a c 87 à CPUs
a b } Memory
June 1, 2007 9:25:07 AM

Okay doky. Sorry you feel that way.
June 2, 2007 7:18:36 PM

Thanks for this informative post.
!