A little FSB/Memory speed help

FrK` · 15 Jan 2007 at 11:33

I little help just to clear things up

When RAM is advertised at 1066mhz DDR2, it means that it actully runs at 533Mhz with the fsb.

If i brought a processer with a fsb of 266, I could effectivley raise the fsb to 533mhz using that ram? (Thats without changing the RAM:FSB ratio or overclocking it)

Thanks

steve258 · 15 Jan 2007 at 12:53

That is right, but it is very difficult to OC the FSB to 533Mhz anyway, not without crazy cooling and extreme volt I think.

Just to confuse you the effective FSB is always 4* the actual FSB, so if you oc it to 533Mhz it will be 2133Mhz effective, while your RAM runs at 1066Mhz unless you run a divider.

NachT · 15 Jan 2007 at 13:17

So there's no point in buying RAM that runs that fast?

Say if you buy some DDR2 PC6400 and some DDR2 PC8500, the 6400 would just be as fast realy? because you couldn't run the 8500 stuff at 1066mhz anyway?

FrK` · 15 Jan 2007 at 13:27

so i would need RAM running at 2000 mhmz :confused:

steve258 · 15 Jan 2007 at 14:03

NachT said:
So there's no point in buying RAM that runs that fast?

Say if you buy some DDR2 PC6400 and some DDR2 PC8500, the 6400 would just be as fast realy? because you couldn't run the 8500 stuff at 1066mhz anyway?

Not if you set a mem divider so the RAM runs faster than the FSB, say if you set FSB:RAM ratio to 1:2 then RAM will be running twice the speed of the FSB, so for example with a stock C2D 266Mhz FSB the RAM will be running 533Mhz, which is DDR2 1066 effective.

FrK` said:
so i would need RAM running at 2000 mhmz

No the effective DDR2 speed is 2* the speed of actual FSB assuming that you run 1:1 ratio. The FSB speed is quad-pumped for Intel ever since the first P4 so the effective speed is 4* faster. So with a standard C2D at stock settings the FSB will be 266Mhz, which is 1066Mhz effective and the RAM will run at 533Mhz effective.

Similar with AMD where you have HT multiplier which is adjustable from 2* to 5* the speed of actual FSB, although the RAM speed is calculated differently.

Hope I explained it correctly cuz I've confused myself too.

NachT · 15 Jan 2007 at 14:13

steve258 said:
Not if you set a mem divider so the RAM runs faster than the FSB, say if you set FSB:RAM ratio to 1:2 then RAM will be running twice the speed of the FSB, so for example with a stock C2D 266Mhz FSB the RAM will be running 533Mhz, which is DDR2 1066 effective.

Isn't there a down side to running the RAM faster than the FSB?

I thought if you ran the FSB:RAM at 1:1 it would be faster, some how?

Or doesn't it make a difference

So it's safe for me to buy 1000mhz+ RAM, and i'll be able to make full use of it?