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FSB vs Memory Clock speed


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#1 Ankit23

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Posted 06 May 2009 - 02:43 PM

Hi, I have P5GC-MX 1333 motherboard. The Motherboard manual says it supports DDR2 553 and DDR2 667. I currently have installed DDR2 667. My question is DDR2 667 runs at 166 MHz. Why cant I use DDR2 800 which runs at 200 MHz to match my FSB of the mobo of 200 mhz.

Second Question: Right now my bios is set to configure eveything automatically. The CPUZ program says FSB to DRAM ratio is 3:5. Can I change my bios to make it run at 1:1 , is this a wise move?

Thanks

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#2 fairjoeblue

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Posted 06 May 2009 - 03:30 PM

Your math is a little off
To get the speed at which DDR2 memory works you have to devide the rayed speed by 2.

533MHz = 266.5 [or 266]

667MHz = 333.5 [or 333]

800MHz = 400

"To get the real clock divide the nominal clock by two. For example, DDR2-667 memory works in fact at 333 MHz. "

http://www.hardwaresecrets.com/article/167

There is also more to memory then just the rated speed.
You have to take into consideration the timings & voltage.

If you are adept at overclocking you could probably install 500MHz memory , which would default to 667MHz , & then overclock it in the BIOS .
In order to do that you have to have a good motherboard that has overclocking features.

A read,
http://www.tomshardware.com/reviews/pushin...max,1081-2.html
OCZ StealthXstream 700W,Gigabyte GA-EP45-UD3R , E8500, Arctic Freezer Pro 7, 3GB G.Skill PC8500,Gigabyte Radeon HD 4850 OC [1GB ], Seagate 250GB SATA II X2 in RAID 0, Samsung SATA DVD burner.

#3 Ankit23

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Posted 06 May 2009 - 09:08 PM

First of all, Thanks for the reply. This prompts me to ask you another question... instead of investing in ddr 667 I would have been better off by using ddr 533.

Because ddr 533 would operate at 266 MHz which is still little faster than my mobo FSB of 200 mhz. Or NO?

with ddr 667 CPUZ reports FSB:SDRAM ratio of 3:5 ( 200 mhz / 333 mhz)

If I underclock my ddr 667 to run at 533...i would get FSB:SDRAM of 3:4 ( 200 mhz / 266 mhz) ... Isn't this better since its close to 1:1 ??

last question... is there any software out there that i can use which would tell me performance difference at different memory speeds?

Thanks a lot for your help.

#4 fairjoeblue

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Posted 07 May 2009 - 07:17 AM

If you have a Core2Duo CPU it has "speedstep" .
Speedstep makes the CPU run slower by reducing the CPU multiplier until the CPU is put under a heavy load then it "revs" up to full speed.

As an example , I have a 2.66GHZ CPU with a 10X multiplier.
In normal operation the multiplier would drop to 6X & the CPU would run at 1.6GHz until the CPU was put under a heavy load, then it went to full speed.
[I disabled speedstep in the BIOS, manually set the multilpier to 10X , & increased the FSB to 320, & run the CPU at 3.2 all the time.]

All of that affects the memory .

Your unit woyld have been a tad slower with 533MHz memory .

You can download PC Wizard & use the Bencmarking feature to compare different memory speeds.

http://www.cpuid.com/download/pcw2008_v1871.exe
OCZ StealthXstream 700W,Gigabyte GA-EP45-UD3R , E8500, Arctic Freezer Pro 7, 3GB G.Skill PC8500,Gigabyte Radeon HD 4850 OC [1GB ], Seagate 250GB SATA II X2 in RAID 0, Samsung SATA DVD burner.




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