I am building a new system and am getting confused about what has to match with regards to cpu, memory speed, and what the motherboard speed is.

For example:

I want to get the ASUS P5E3 (http://www.newegg.com/Product/Product.aspx?Item=N82E16813131276) and it lists the memory standard as DDR3 2000(OC)/1800(OC)/1600 and FSB as 1600/1333MHz.

I want to get the Intel Core 2 Quad Q9450 proc (http://www.newegg.com/Product/Product.aspx?Item=N82E16819115042) and it lists its FSB at 1333MHz.

So do I get DDR3 1600 or 1333 speed memory?

I was looking to get OCZ Reaper HPC 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 memory. (http://www.newegg.com/Product/Product.aspx?Item=N82E16820227320)

I do not plan to overclock at all. I plan on running 2 ATI 4870's in crossfire mode -- please let me know if this is a viable rig...

Much thx,
rhugga

whoa whoa. im surprised no one responded to you yet

i just read your post, and saw your DDR3 1600 memory? my god, that would have been like a few hundred bucks wasted if you didn't do the proper research.

i feel like i typed up info like this so much on this forum already but here goes again.

DDR2 memory is "doubled pumped"...
FSB is "quad pumped"... so just leave that as is right now

the Q9450 has a FSB (front side bus) of 333mhz.

so...333mhz (fsb) x 4 (quad pumped) = 1333mhz (FSB frequency)....so that is where the number 1333mhz came from

your CPU frequency is determined by the multiplier of the CPU x FSB ...so for the Q9450 at stock, it is 333mhz (fsb) x 8 (multiplier)....that would equate to 2.66ghz (cpu frequency)

so....now...ram is doubled pumped. DDR2 anyways...and that is what i suggest you buy as DDR3 is a complete waste of money, until nehalem...but thats a different story

so to keep it simple, the memory that you need to be able to run 1:1 ratio with your CPU is basically, the FSB frequency/2 = your ram # mhz

so for a stock Q9450, 1333/2 = 667mhz ram would run 1:1 with it

so when you overclock, if you ever plan to, people usually does it through the FSB in LGA775 socket computers.

so lets say you raise the FSB from 333mzh to 400mhz. your FSB freq. would now be 400x4 = 1600mhz, so you're confusing this number with the mhz frequency that you need for your ram. they are two different numbers. the ram mhz and the fsb frequency.

when you are running at 1600 fsb freq, you would only need 800mhz ram

1600/2 = 800mhz.

DDR3 1600 and 1333 are for like future computers such as the nehalem core which would be using those only. but that is ram frequency, they have the same numbers but dont' get confused...

DDR2 = 533mhz, 667, 800, 1066mhz and so on...

DDR3 = 1333 mhz, 1600mhz...

so basically the thing that you were confused about is that you thought ram mhz and fsb freq had to match 1 for 1, but you didn't know that ram is doubled pumped and fsb is quad pumped.

667 x 2 (doubled pumped) = 1333mhz. so 667 is the ram you would need to run your Q9450 at 1:1 ratio.

phew, hope that clears things up for you.

Yeah, get a mobo that takes DDR2 and get DDR2 800, because you probably will want to OC sooner or later. Don't waste the cash on DDR3.

Get this or this and some DDR2 800 that was suggested earlier like this. DDR3 boards are expensive and DDR3 is immature and very expensive and doesn't provide any performance gain over DDR2.

For a 1:1 ratio get the DDR3 1333Mhz (667MHz) memory. If you get the DDR3 1600 (800MHz) memory you would need a processor with 1600 FSB to run 1:1.

I haven't kept up with the advances of the latest and greatest chipsets but I read a review from anandtech a while back showing the difference between ddr2 and ddr3 and remember reading the difference was only a few percentages. I know the review was between a p965 and P35 chipset. Review link is below. Especially take a look at the section titled "What is DDR3?".

http://www.anandtech.com/memory/sh [...] i=2989&p=1

I don't know all the new features of the x48 but I'm sure some smart people here can give you the pros and cons of it.

The reason I bring this up is because DDR3 memory is so much more expensive compared to DDR2 from what I've seen. If you are trying to meet a budget I would say rethink it (and the board of course), but if you have the cash go for it and enjoy those 4870s in CF!

Nope, assuming a standard dual-channel setup, DDR3-1333 would be in a 1:1 throughput ratio with a 2666MHz throughput FSB, and DDR3-1600 even a faster FSB.
DDR2-800 (can handle up to 1600MHz FSB throughput) is plenty for almost everyone.

Thanks aznguy0028! Your answer is helping me understand this FSB/RAM thing and hopefully not fall into the DDR3 buying when I really don't need it. I'm building a system around an Intel Core 2 Extreme QX9650. It has a FSB of 1333 Mhz and 3.0 Ghz CPU, so from what I understand I should use DDR2 667Mhz correct? Is there any advantage if I use DDR2 800 or 1066? Will I get more out of it if I do, or will I just upset the processor since I'm messing the 1:1 ratio?
Thnx,

ache75

One thing you have to keep in mind is that a lot of memory has multiple settings, most of which you don't know about until you buy it. Take for instance this is a shot from my old memory which was sold as DDR2 800 4-4-3-10

As you can see there are multiple JEDEC and EPP (Enhanced Performance Profiles) settings which can be as low as DDR2 667 3-3-3-10. Since you are buying an Extreme CPU and you will have the option of increasing the multiplier you would be fine purchasing either but I would suggest going with DDR2 800 and if your using a FSB lower than 1600 you can always underclock the memory and tighten the timings.