deciding between two different mobo/RAM combos

[OOBradm]

Like the summary says, I am deciding between two different combos of mobos/ram... I have

ASUS P5K (p35 chipset)
DDR2 1066 2x 1gb

EVGA 650i ultra (nforce 650i chipset)
DDR2 800 2x 1gb

The first combo listed is roughly $150 more than the second. Will the performance boost be worth the additional cost? One thing I keep thinking about is how the ddr2 1066 in the first combo will sync with the 1333 FSB of the P5k with a nice 1:1 ratio, whereas the 650i ultra and the ddr2 800 has some strange 1:1.33 ratio. Thoughts?

 

[MarcVenice]

There's no need to buy ddr 2 1066 combined with the asus p5k. I'd mix those combo's hehe, asus p5k, great mobo, with ddr 800. Coz no the extra cost will not be worth the very minor performance boost. Even a 1333fsb cpu will run at least 1:1 with ddr 800. Anything higher doesn't really result in noticable performance gains. Putting the extra money towards another 2gb of ram will yield you a significant performance boost though.

 

[OOBradm]

care to explain the FSB to memory ratio for me?

My understanding was this:
the P5K has a QDR 266mhz fsb.
DDR2 1066 ram has a 266mhz core clock and essentially a 4x multiplier due to the double data rate.

So these two would run at a 1:1 ratio.



DDR2 800 runs at 200mhz, which is effectively 800mhz due to double data rate.
this doesn't sync with the 266mhz QDR FSB, since 266 / 200 is 1.33

Care to correct me on my understanding if need be?

 

[MarcVenice]

nah, the ddr 2 1066 is double pumped, if your cpu's fsb would be at 533 * which no cpu's are *, or 2166fsb when qaudpumped, then it would run 1:1 with ddr2 1066mhz.

For a cpu with a fsb at 266, you could actually buy cheap ddr2 533mhz and still have it run 1:1 with your CPU. The newer cpu's have a 1333fsb though, which thus need ddr2 667mhz to run 1:1. Ddr 800 is a little overkill if you look at it like that, and will run at 1:1 or better.

I think that's the easiest way to explain it. I don't know all the ins and outs though, that's just how it is. I suppose if you look on the ram forum people can give you more detailed explanations though.

 

[JustaGeek]

For 1066MHz memory speed with the 266MHz FSB, the memory divider is 2.

266.7MHz (FSB) x 2 (memory divider) = 533MHz (Memory Bus) x 2 (DDR2 - Double Data Rate 2nd Generation) = 1066 MHz (Memory Speed.)

 

[SerpentRoyal]

Core speed is KING. 650i runs hot and require modification to NB and SB if you intend to push FSB above 300MHz. Go with high quality DDR2 800 rated at 1.8V. You should be able to push memory speed up to at least 450MHz with 2.0Vdimm. Higher memory speed will only marginally improve system performance.

 

[OOBradm]

"The key difference between DDR and DDR2 is that in DDR2 the bus is clocked at twice the speed of the memory cells, so four words of data can be transferred per memory cell cycle. Thus, without speeding up the memory cells themselves, DDR2 can effectively operate at twice the bus speed of DDR." - wikipedia

This confuses me, especially where it says "the bus is clocked at twice the speed of the memory cells". Is it talking about the FSB? I'm thinking that is wher JustaGeek got his memory divider number from, but I don't fully understand how it works.

Per say I have a machine with 200mhz FSB. Then DDR2 400 would run at 1:1, right? also, DDR 400 would also run 1:1. But the difference is the core clock of the DDR2 is 100mhz, and the core clock of DDR2 is only 100mhz (according to wikipedia). so i guess DDR2 has the ablity to run its memory at half the FSB clockrate? is this correct?

 

[OOBradm]

and one more question, how important is it to have a 1:1 ratio of FSB to core memory clock speed. Will performace actually decrease if i get RAM with a higher core clock than the FSB?

as in, I have a 200Mhz FSB,
and I have the option of DDR2 400 (200mhz core)
or DDR2 533 (266 mhz core)

will the DDR2 400 actually perform better?

 

[MarcVenice]

No the ddr400 will not perform better, but neither will the ddr2 533, or not much at least, a negligible performance boost might be obtained but that's it ...

 

[OOBradm]

Originally posted by: MarcVenice
No the ddr400 will not perform better, but neither will the ddr2 533, or not much at least, a negligible performance boost might be obtained but that's it ...

in comparison to what?