Is there has big difference between Single and Dual Channel mode when running 2x1GB ram with vista 64bit ?
thx

Yes, it's twice the bandwidth/speed.

I am sorry, but is it only in theory, Or is it really twice times faster in actual performance?
thx

It will depend on who/what you ask. PCMark will show a lower memory score, as will Sisoft sandra. Games will care a lot less, as they don't depend on just the memory to work. (meaning CPU and GPU also come into play.) If my memory serves, most systems will see a 5-10% drop in performance. this means instead of seeing 60FPS in X game, you'd have 57. Its not like if you went to single channel you'd see 30FPS.

Most apps tend to be CPU or GPU bound, those that need lots of memory will show the biggest loses. Also, seeing as AMD CPUs are so memory dependent, I'd expect them to show larger losses then Intel CPUs.

If you run apps (encoding, decoding, A/V editing, etc) that require a lot of memory bandwidth, regardless of the OS, dual channel will make a difference.

It does make a difference. However, most people would never actually notice the difference. I don't know how many people run out and buy a single new stick of memory, pop it in their PC, and then proclaim how much better it is with their new memory, not realizing they just disabled dual channel mode.

What 4745454b says is right. The actual performance drop in everyday apps and games will be 5-10%. If you run memory intense apps you will see a bit more of a difference

It'll be more than 5-10% difference. We're not talking about already high speed ram running at greater than 1:1 ratio, with the extra speed wasted, compared to slower ram. Cutting a typical 800mhz ddr2 @1:1 ratio into single channel will have real consequences. Another thing is, 1200mhz to 800mhz is almost identical in real world performance, but 800 to 400 can perform significantly different, despite the same 400 drop. It's a matter of how low can you go without bottlenecking. For recent cpus and typical ram, single channel is too low.

So let me guess, if you set up an AID0 array your harddrive scores will double? Care to show any links?

http://www.anandtech.com/cpuchipse [...] i=2330&p=3

That's wrong. A single core Athlon 64 is too slow to show significant bottlenecking. Don't use old reviews

Where's your link? Show me how I'm wrong, don't just say so.

It's not like I didn't try. Can't find any. No one test single vs dual channels anymore with modern quads.

People take dual channel for granted those days.

In which case, I will continue to go with what I've seen. Single channel will slow things down by probably at least 5%, though more is likely depending on the task. If the task is memory sensitive, then you'll see more like 10-20% less speed. For gaming, your probably looking at 10% on average, just like my link showed.

You have to remember that while doing X task, there is more then just memory read/writes. There is a lot of CPU time involved, and transfers to/from the harddrive and video card. Just because you slow the memory (or link another harddrive in an AID0 array) doesn't mean your scores for something will change. Single channel WILL slow your performance, but it won't cut it in half, it probably won't slow you down by even 25%.