Why Dual Channel Memory?

[travistee]

I started a thread in the Intel category
http://forums.windrivers.com/showthread.php?t=73842

about dual channel memory but now I looking at an ASus board that supports 800Mhz memory 240pin.

Seems that dual channel is supposed to give a 5 -15% performance increase.

Now looking at the prices I can get
DDR2
Ultra 800MHz PC6400 2 x 512MB $199.99
Ultra 533MHz PC4200 2 x 512MB $92.99
Ultra 800MHz PC6400 2 x 512MB $199.99
Corsair 667MHz PC5400 2 x 512MB $204.99

dual channel
Crucial 400MHz PC3200 2 x 512MB $173.99

Would I get better performance getting 2GB of the 533 instead of 1GB of the 800?

I read that I don't really need memory sold as "dual channel" just two sticks of identical ddr2.

So can I just get the ddr2?
Am I supposed to use the pair of 400MHz or can I use the pair of 800MHz (1gb for $199), or can I use 2 pair (4) of the 533 (2gb for $184)?

If I can get 2GB for $200 and it will not run as "dual channel" will I get better performance that 1GB that does run as dual channel?

I'm still confused about if I need to use 2 400Mhz sticks when the board supports 800MHz in dual channel or can I use 2 800MHz sticks?

[travistee]

The asus motherboard I am getting is the P5WD2.
It has a 1066FSB.

[rgharper]

In theory, two sufficiently-closely-matched memory modules will work in a dual-channel system even if they aren't sold as a matched pair. The reason that the dual-channel packages fetch a higher price is because they are generally the higher-quality memory that a vendor sells and are guaranteed to work in a dual-channel board. Buying two "off-the-shelf" modules will probably work but there's no guarantee - and as long as the module works you probably won't be able to exchange it just because it won't work in dual-channel mode.

[TripleRLtd]

In theory, two sufficiently-closely-matched memory modules will work in a dual-channel system even if they aren't sold as a matched pair. The reason that the dual-channel packages fetch a higher price is because they are generally the higher-quality memory that a vendor sells and are guaranteed to work in a dual-channel board. Buying two "off-the-shelf" modules will probably work but there's no guarantee - and as long as the module works you probably won't be able to exchange it just because it won't work in dual-channel mode.

Hence, why it makes much more sense for people not in the business to just buy matched/guaranteed ram.