How to calculate FSB on Quad Core?

[dpapag]

I'm trying to understand how the math works to arrive at the numbers below When dealing with a Q6600 quad core in Ram/FSB 1:1 ratio:

QDR = effective FSB speed


CPU FSB QDR Multi RAM Final MHZ
Q6600 266Mhz 1066QDR 9x 533Mhz 2400Mhz
Q6600 333Mhz 1333QDR 9x 667Mhz 3000Mhz
Q6600 400Mhz 1600QDR 8x 800Mhz 3200Mhz
Q6600 375Mhz 1500QDR 9x 750Mhz 3375Mhz
Q6600 450Mhz 1800QDR 8x 900Mhz 3600Mhz
Q6600 400Mhz 1600QDR 9x 800Mhz 3600Mhz


Since ram is double the data rate:
DDRMhz= 2 x RamMhz : FSBMhz x 4 =QDR) = 1:1

How does this equation change when a 1:2 ratio is taken into account?

If the math for 800Mhz ram in 1:1 ratio is: DDR800= 2 x 400Mhz : 400Mhz x 4 = 1600QDR) = 1:1 =3600Mhz

1. How does the math work out for DDR1600 ram in 1:1 ratio?
2. How does the math work for DDR1600 ram in 1:2 ratio?

 

[Theocnoob]

Your bios answers all these questions for you. That's the fun part. You don't have to be smarter than a fifth grader to win.

I also don't fully understand the question.

 

[Automata]

The number of cores has nothing to do with the calculations and neither does the RAM.

QDR stands for Quad Data Rate, or "Quad-pumped". Divide by four to get the FSB and multiply by the multiplier to get the final speed.

1600 QDR / 4 = 400 FSB * 9x multi = 3600 MHz

So, if the RAM was running at 1:1 with these settings:
400 FSB * double data rate = 800 MHz

 

[dpapag]

I'm trying to figure out if this math is correct assuming a 9x multiplier in both cases.

1600Mhz ram in 1:1 ratio is: DDR1600= 2 x 800Mhz : 800Mhz x 4 = 3200QDR) = 1:1 =7200Mhz

1600Mhz ram in 1:2 ratio is: DDR1600= 2 x 400Mhz : 400Mhz x 4 = 1600QDR) = 1:1 =3600Mhz

 

[Automata]

No, not even close. You have to multiply by the base FSB, not the QDR.

 

[Evilsizer]

lets keep it simple for right now, if using a 1:1 ratio between fsb and ram it would look like. ie 400mhz fsb, ram speed 400mhz SDR, then for DDR equals 800mhz, the DDR2-800 is the final speed there is no more doubling.

the ram speed you listed is final ram speed, ie DDR2-533 ect ect... the only way to get to a 1600mhz on ram speed is if your board uses DDR3 ram. from what you listed your board only supports DDR2, not only that but there is no DDR2 rated to run at 1600mhz.

 

[dpapag]

The number of cores has nothing to do with the calculations and neither does the RAM.

QDR stands for Quad Data Rate, or "Quad-pumped". Divide by four to get the FSB and multiply by the multiplier to get the final speed.

1600 QDR / 4 = 400 FSB * 9x multi = 3600 MHz

So, if the RAM was running at 1:1 with these settings:
400 FSB * double data rate = 800 MHz

What if the ram being used is DDR 1600 at a 1:2 ratio at a 9x multi?
Something like CORSAIR Dominator CM2X1024-8500C5D

 

[Automata]

First off, that isn't 1600 MHz, it is 1066 MHz. To run a 1:2 ratio, you'd have to be running 266 MHz FSB.

 

[Evilsizer]

the 9x multi of the cpu has nothing to do with the ram speed at all. the cpu speed at 9x is derived from the fsb speed. the 1:1 or any ratio is defined as the following FSB:RAM, so this ratio you talk about has nothing to do with the cpu's speed.

im tring to make sure you have it clear as to what effects what.

 

[dpapag]

First off, that isn't 1600 MHz, it is 1066 MHz. To run a 1:2 ratio, you'd have to be running 266 MHz FSB.

Got it. So what happens if you try to run that Corsair ram which is 1066Mhz in a 1:1 ratio? Wouldn't it be unstable because the FSB would be too high at 533Mhz?

DDR1066= 2 x 533Mhz : 533Mhz x 4 = 2132QDR = 1:1 = 4797Mhz

533Mhz * 9 = 4797Mhz (not gonna happen with a Q6600)

2132 QDR / 4 = 533 FSB * 9x multi = 4797 MHz

So, if the RAM was running at 1:1 with these settings:
533 FSB * double data rate = 1066 MHz

What's confusing me is a something that I read which said:
"People buying DDR1066 Ram are wanting to run it 2x as fast as thier FSB, or a 2:1 ratio. This is rarely beneficial, you will notice most of the people with good overclocks are running close to a 1:1 ratio."

How can a good overclock be had at a 1:1 ratio with 1066Mhz ram when it causes the FSB to be too high at 533Mhz? I'm assuming my math is wrong somehow?

 

[MattNo5ss]

You concentrate on the CPU speed and let the RAM speed fall where it may.

A Q6600 will probably only get around 3.6-3.8GHz (400-423MHz FSB) for 24/7 use, YMMV of course. So, if you want your CPU at 3.7GHz, then the RAM will just run at 824MHz (2*412MHz) in a 1:1 ratio. Once you have the CPU where you want it, then try increasing the RAM speed to see if you can get it stable.

So, work on the CPU speed first, then RAM speed. Not RAM speed, then CPU speed.

 

[Automata]

I agree with what Matt said. If you aren't running the RAM at full speed after getting your optimal CPU speed, lower the timing.

 

[dpapag]

Understood. Doing some research, I see alot of 1066Mhz RAM being used with the Q6600. Why go that high on RAM when it's not going to be able to run much higher than 800Mhz on that CPU on an aggressive overclock from 2.4 to 3.6, being that the 1:1 ratio is reported to be the most stable?

 

[Automata]

You can lower the timings, which effectively does the same thing as upping the MHz.

 

[RGone]

DDR1066= 2 x 533Mhz : 533Mhz x 4 = 2132QDR

The problem is that here is NO QDR that has any relation to the ram speed whatsoever. Ram of today is called DDR or Double Data Rate meaning that transfers are made on the rise and fall of register change.

One more time there is nothing about QDR or Quad Data Rate that is in anyway related to the speed of the ram. Nada.

EDIT: back to your original post where you write this >> QDR = effective FSB speed << and that is totally incorrect when calculating cpu speed or ram speed. QDR divided by four equals what we have called for years the FSB. Now Intel's QDR or Quad Pumped number divided by four equals the number to muliply by the CPU multiplier to get the cpu Mhz.

So a 1066QDR cpu like the Q6600 would get its' speed by dividing 1066 by 4 which equals 266 times 9 multiplier and the cpu speed is then ~2400Mhz.
As for the ram if the ram multiplier was set to 1:1 then the ram speed would be 266 since 1066/4 = 266 and the ram multiplier is 1 then the ram speed is 266 but being DDR (double data rate) the actual 'working' ram speed is 2 x 266 = 533 DDR. (double data rate) END EDIT.

 

[dpapag]

All clear now! Thanks to everyone that responded.

 

[MattNo5ss]

The whole reason to use faster RAM is so you won't have to OC the RAM as well to get a certain FSB. If you had a newer LGA775 CPU like Wolfdale or Yorkfield, then they can easily do more than 400MHz FSB, which exceeds DDR2-800. So, higher than DDR2-800 is preferred for the newer chips, and DDR2-1066 is the most common next step up.

 

[Automata]

Yeah, Wolfdale was awesome.

http://i55.photobucket.com/albums/g121/thideras/Benches/e3110/9984-4673.png
http://i55.photobucket.com/albums/g121/thideras/Benches/e3110/580.png?t=1242321746

I actually had to switch to DDR3 because DDR2 RAM (D9's even!) were holding me back.

 

[MattNo5ss]

Yeah, Wolfdale was awesome.

http://i55.photobucket.com/albums/g121/thideras/Benches/e3110/9984-4673.png
http://i55.photobucket.com/albums/g121/thideras/Benches/e3110/580.png?t=1242321746

I actually had to switch to DDR3 because DDR2 RAM (D9's even!) were holding me back.

Oh yeah, DDR3 was almost required for really high FSB on the duallies, DDR2 D9 would suffice for the Yorkfields though.

 

[Automata]

Yeah, they did pretty horrible in that regard.