sdram, rdram, ddram, ECC, registered.. wot?

with my vendor, i can choose from the following memory:

SDRAM
SDRAM ECC
SDRAM Registered
DDRAM
DDRAM ECC
DDRAM Registered
RDRAM
RDRAM ECC

wots the difference between all this??

SDR RAM = Single Data Rate RAM - older versions of RAM sticks transfer data once per clock cycle.

DDR RAM = Double Data Rate RAM - transfers data on both the rising and falling edges of the clock pulse.

ECC = Error Checking Capability or something - extra chip on the RAM stick holds parity data for the other 8 chips. It provides error recognition and correction.

Registered = Each RAM chip usually has it's address and control wires fed directly from the Chipset. However putting lots of RAM sticks into a motherboard means the chipset has to drive lots of chips, and consequently the load on the chipset drive transistors increases, causing errors. Registered modules have a buffer on each stick that processes the signals coming in so the chipset has to only drive 1 address and control bus to each stick. In servers running 4GB of memory this becomes a necessity.

RDRAM - an outdated and becoming-obsolete version of SDR memory used with pentium 4 motherboards.

correction rambus' life depends on the success of ddr2,(which is a higher clocked version of ddr) rambus is supposed to come out with like a dual channel pc1260 or something and is supposed to have the best mem bandwith available. I dont know about it, my opinion is, it had better go up in clocks fast and drop prices fast to become a competitor.