Question : Problem: Difference between DDR and RD RAM, and recommendation for new system?

I am looking for an explanation as to the difference between RD (Rambus) RAM and DDR (double data rate) RAM.  I know RD is a lot more expensive.  Perhaps a user could point me to a website or article on the subject.  I am considering buying a new MB/CPU for my PC and I have a choice between RD and DDR.  I have been told Rambus is better for server applications and DDR is better for PC use.  I am not much of a gamer and I do not do photo or movie editing.  I do run some pretty heavy duty analysis (simulation) SW on a stand-alone PC.  I want the fastest overall response.  

When you frame your answers please consider that I consider myself to have a novice to moderate level of understanding of how memory works.

Thank you

Answer : Problem: Difference between DDR and RD RAM, and recommendation for new system?

A big difference that made RDRAM desirable (once, but not now) was one of bandwidth.

When DDR first came on the market, it was running at a maximum of 2.1GB/s of bandwidth.  RDRAM at the time was doing 3.2GB/s.

Now, however, if using Dual-DDR PC3200 you can get a maximum of 6.4GB/s (PC3200 @400MHz, Dual-Channel) which is superior to that of RDRAM's PC1200-Dual 4.8GB/s.

Also of note, DDR RAM is much less expensive than RDRAM.

How The Two Systems Differ and General Summary

This is taken from overclockers.com:  

"RDRAM is a narrow, high speed serial connection.
SDRAM/DDR is a wider, lower speed parallel connection. (DDR is simply SDRAM that squeezes out two actions per clock cycle; something RDRAM already does. I'll use the term "SDRAM" when what I'm saying applies to both current SDRAM and DDR, and "DDR" when it applies only to that).

Just about all the major advantages and disadvantages between RDRAM and SDRAM stem from this difference.
These are two much different ways of handling data flow. RDRAM does a little very quickly. SDRAM does much more but more slowly.

The wiring on RDRAM modules is technically more challenging, but there is much less of it. It operates best with simple configurations; performance degrades as you add more devices. This is typical of serial devices. "