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FSB question, confused, plz help

Last response: in CPUs
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June 17, 2010 12:03:38 AM

Hey guys , im about to put a rig together from parts that i have kicking around.

cpu= Q6600
ram= 2x1 gb pc2 5300 and 2 x 512mb pc2 6400 (3 gigs total)

i know since some of the ram is 533 mhz it will pull the faster 667 mhz ram down to 533, the q6600 has a 266 mhz x9 bus speed correct?

so the bus speed of the cpu will be 266 and the bus speed of the ram will be 533? making it a 1:2 ratio?

im sorry if im making no sense, this is just what ive kinda gather from looking around but i havent found a clear explanation of how this works, plz chime in and let me know.
June 17, 2010 1:22:08 AM

anybody?
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a c 172 à CPUs
June 17, 2010 6:02:09 PM

Definition time (attention purists, I'm talking about DDR2 and I'm simplifying a little :) ):
Core2 CPU's use a frontside bus (FSB). The FSB is a thing with two main characteristics: speed which is usually defined in MHz and width which in the Core2's is 64 bits wide. We are concerned with the speed.

Using the Q6600 as an example, the FSB frequency is 266 MHz. The matching DDR2 memory clock for that frequency is 533 MHz (266 X 2). DDR2 memory transfers two chunks of data for each bus cycle, hence double the frequency. So, to run 1:1 at an FSB of 266 MHz, we need DDR2-533 RAM. What CPUZ does is a little confusing. It will tell you that the memory frequency is 266 MHz for a 1:1 ratio.

The FSB clock is 1066 MHz (266 X 4). The bus is "quad pumped". It transfers 4 chunks of data into and out of the CPU each cycle. So each FSB cycle generates 4 FSB clocks.

Now, if you increase the FSB frequency to 333 MHz, the corresponding memory clock is 667 MHz and the FSB clock is 1333 MHz.

I always run my memory at 1:1. That is the FSB freq to mem freq ratio of one to one. That means that the memclock is twice the FSB freq. It's a little confusing. Running memory slower costs performance. Running memory faster does not give you much if any real world performance increase and it can lead to higher instability.

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June 17, 2010 9:26:02 PM

Best answer selected by sean1986.
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June 17, 2010 9:26:39 PM

jsc said:
Definition time (attention purists, I'm talking about DDR2 and I'm simplifying a little :) ):
Core2 CPU's use a frontside bus (FSB). The FSB is a thing with two main characteristics: speed which is usually defined in MHz and width which in the Core2's is 64 bits wide. We are concerned with the speed.

Using the Q6600 as an example, the FSB frequency is 266 MHz. The matching DDR2 memory clock for that frequency is 533 MHz (266 X 2). DDR2 memory transfers two chunks of data for each bus cycle, hence double the frequency. So, to run 1:1 at an FSB of 266 MHz, we need DDR2-533 RAM. What CPUZ does is a little confusing. It will tell you that the memory frequency is 266 MHz for a 1:1 ratio.

The FSB clock is 1066 MHz (266 X 4). The bus is "quad pumped". It transfers 4 chunks of data into and out of the CPU each cycle. So each FSB cycle generates 4 FSB clocks.

Now, if you increase the FSB frequency to 333 MHz, the corresponding memory clock is 667 MHz and the FSB clock is 1333 MHz.

I always run my memory at 1:1. That is the FSB freq to mem freq ratio of one to one. That means that the memclock is twice the FSB freq. It's a little confusing. Running memory slower costs performance. Running memory faster does not give you much if any real world performance increase and it can lead to higher instability.



Awsome , thx for that great explanation , so basically if I leave my q6600 at the stock speed of 266mhz and i have 533 mhz ram then i will be running at a 1:1 ratio correct? and that will be the best setup i could achive with the hardware i have?

if i were to overclock my q6600 to 333 mhz would that be hurting my overall performace seeing how my ram is only 533 and not 667?
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June 17, 2010 9:31:53 PM

or could i overclock my ram to 667mhz to keep up with the 333mhz?
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