does iPhone4 run 2-time faster than iPhone 3GS since iPhone4's memory is 2-time bigger than iPhone 3GS's one I have never tried any iPhone, but want to research about it.

Apple said that "iPhone 3GS" is  2-time faster than "iPhone 2G" since 3GS' memory is 256 MB eDRAM &amp; thus is twice as big as 3G's (128 MB eDRAM)

In turn, iPhone 4's memory is "512 MB DRAM", so my question is 

does iPhone4 run 2-time faster than iPhone 3GS since iPhone4's memory is 2-time bigger than iPhone 3GS's one?

Also, eDRAM and DRAM is almost the same? or they have any difference?
No. Well.... maybe.
Although the phone may run twice as fast (I don't know, I don't have any iPhones), it is not the addition of memory that makes it run faster. If the phone was running out of memory and had to kill processes, then more memory would make it seem faster.

What really makes phones, (or any computer-like device for that matter) run faster, is a fast processor. The iPhone 4 also has a faster processor than the 3GS.