Dual Channel VS Single Channel RAM - system performance difference?

Hello All!

I am a little confused about the whole single vs dual channel ram concept. I know that dual is better than single, performance wise, but by how much?

I guess I should outline the current scenario for you. My partner's computer is quite slow. It's running a 2.66GHz Northwood, with 533MHz FSB and 512KB L2. It's also got 512MB RAM in the form of 2 modules of 256MB, running at "dual channel" DDR266. Now my partner is getting frustrated with the slow speed of her computer and I happen to have (lying around from a build that never took place) an ASRock MB, 512MB (single module) of DDR400 RAM and a 3.2GHz Prescott (Skt.478).

I was thinking that I could just install the ASRock motherboard with the RAM and CPU that is on it, replacing my partners existing northwood set-up. Because her current motherboard wont run Prescott core P4's, it's either install the ASRock board with the Pressy on it, or buy a new board...

So, I guess what I am actually trying to ask (excuse me, I am very tired right now) is how much of a performance increase is she likely to see going from this set-up:

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2.66GHz Northwood, 512KB L2, 533MHz FSB, No Hyperthreading
512MB DDR266 RAM (2 x 256MB Modules) in "dual channel" (533MHz)
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to this set-up:
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3.2GHz Prescott, 1024KB L2, 800MHz FSB, with Hyperthreading
512MB DD400 RAM (1 x 512MB Module) in "single channel" (400MHz)
--------------------------

OK, yes, obviously the processor will be 540MHz (20%) faster and it will have 2x as much L2 cache AND will utilise Hyperthreading, but the RAM's total speed (due to being in single channel) will be 133MHz (25%) slower... What will this overall slower ram bus speed mean for the overall performance of the system? Will it actually be worth the hassle of installing the Prescott set-up for my partner, or will she notice a significant increase in overall system performance with the Presscott set-up installed? I don't know...

I just dont know how big a role the bus speed plays in overall system performance... If the CPU bus speed is 800MHz (as it is with the prescott) but the total RAM bus speed is only 400MHz (due to being in single channel) what system bus speed is the system running at? Is it 400MHz, or 800MHz with the RAM taking twice as long as other system components to do its job, or some intermediate speed?

I would appreciate (and rep) any help you can give, either about the two systems compared above, or the dual channel / single channel concept specifically.

Thanks for your help guys!

Highly-Annoyed

Thanks for your quick reply pbasil1

I think that the Prescott set-up will probably be better too, but I'm still a little confused about the RAM speeds involved.

As I understand it, both DDR and dual channel increase the RAM's bandwidth and therefore the overall system performance.

So, DDR266 has an actual speed of 133MHz, which is doubled by DDR (DDR - double data rate) to 266MHz. When 2 (matched pair) DDR266 RAM modules are used together in dual channel mode, this 266MHz RAM bus speed becomes 533MHz, which is, the bus speed of the CPU (in this instance).

With the DDR400 RAM however, although we get the benefits of DDR, making the RAM bus speed 400MHz instead of its actual 200MHz, because we're not using it with another matched module of DDR400 in dual channel, but only using it in single channel on it's own, its total bus speed will only be 400MHz, half of the CPU's (in this instance) bus speed of 800MHz and 133MHz (25%) lower than the RAM bus speed of the Northwood system...

I think I've got this right, but I'm still not sure and even if I have got it correct, I wonder how much different there is between dual and single channel and how much that difference will effect the overall system performance...?

You are probably correct when you say the Prescott set-up will be faster than the Northwood, I just wonder how much performance I loose by having only single channel DDR400 rather than dual channel and what actual difference this will make.

Thanks again for your replay and reps for you!

Highly-Annoyed

OK, you're probably right. Thanks Again!

Highly-Annoyed