ces wrote:Faster Memory - What good is it?
Faster memory can benefit overclockers.
Intel motherboards clock the RAM at some ratio of the FSB speed, aka the memory divider. Many boards are limited to 3 standard memory dividers for FSB200 CPU's: 1:2, 3:5, and 3:4. CPU's with other FSB's (266, 333, etc) will have slightly different dividers.
You calculate your RAM clock like this:
For divider X:Y
(FSB * Y) / X
Example for FSB200 and 1:2 divider: (200 x 2) / 1 = 400 MHz RAM clock
Completing the table for 200 MHz FSB CPU's:
Code: Select all
DIV FSB:MEM EFF MEM SPD
--- --- --- ------------
1:2 = 200:400 (= DDR2 800)
3:5 = 200:333 (= DDR2 667)
3:4 = 200:267 (= DDR2 533)
DDR2-800 can only run as fast as 400 MHz (times 2 because it's ddr2 = the "800" in the spec).
So with a FSB of 200 MHz, and the standard memory divider 1:2, this RAM would run at 400 MHz.
That's fine if you're not overclocking. If you intend to overclock by increasing FSB, you either have to slow down your RAM clock to keep it under 400MHz, or buy faster RAM.
You slow down the RAM clock by picking different memory dividers.
@ 266 FSB you need the 3:4 divider to keep the RAM within spec:
Code: Select all
DIV FSB:MEM EFF MEM SPD
--- --- --- ------------
3:4 = 266:355 (= DDR2 709)
@ 300 FSB you need the 3:4 divider to keep the RAM within spec:
Code: Select all
DIV FSB:MEM EFF MEM SPD
--- --- --- ------------
3:4 = 300:400 (= DDR2 800)
@ 333 FSB you need either a 1:1 or 5:6 divider (not offered on my motherboard for FSB200 CPU's):
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DIV FSB:MEM EFF MEM SPD
--- --- --- ------------
1:1 = 333:333 (= DDR2 667)
5:6 = 333:400 (= DDR2 800)
Because many motherboards limit available dividers based on the
original FSB of the CPU, some people BSEL mod their CPU's. This entails using foil or a silver pen to "draw" a connection between 2 pins on the CPU. It tricks the motherboard into booting at a higher FSB. This *does* unlock other memory dividers, but also voids your warranty and can damage your CPU.
So I don't do that. It's easier and less risky to just buy RAM rated for higher clock speeds and use standard memory dividers.
Moving to DDR2-1066, you can clock up it to 533 MHz.
Completing the table for a 200 MHz FSB at various FSB overclocks:
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DIV FSB:MEM EFF MEM SPD
--- --- --- ------------
1:2 = 240:480 (= DDR2 960)
1:2 = 266:533 (= DDR2 1066) *PERFECT*
1:2 = 333:666 (= DDR2 1333) *Unstable
3:5 = 240:400 (= DDR2 800)
3:5 = 266:443 (= DDR2 887)
3:5 = 300:500 (= DDR2 1000) *Stable, but slower than RAM's rated speed
3:5 = 333:555 (= DDR2 1110) *22 MHz RAM overclock = probably stable
3:4 = 266:355 (= DDR2 710)
3:4 = 300:400 (= DDR2 800)
3:4 = 333:444 (= DDR2 888)
3:4 = 400:533 (= DDR2 1066)
Aiming for FSB 266 should be easy on most motherboards, and will keep DDR2-1066 within spec using the default 1:2 divider.