difference between RDRAM and DDR

[nissmo300]

I bought a gateway computer about 3-4 years ago. It was "top of the line" at the time. It came with 1 GB of RDRAM PC800. How fast or different is this say to 1 GB DDR PC3200?

Here is a pic CPUID

 

[SimGuy]

RDRAM & DDR SDRAM utilize completely different signalling technologies, and hence are incompatible.

RDRAM in PC800 Dual-Channel mode offers 3.2 GB/sec of memory bandwidth, perfectly matched for the 400 MHz FSB P4 systems and 133 MHz FSB P3 systems of the day.

DDR SDRAM in PC3200 Dual-Channel mode offers 6.4 GB/sec of memory bandwidth, perfectly matched for today's high-bandwidth 800 MHz FSB P4 systems and AMD Athlon 64 systems.

DDR SDRAM is a Serial technology, meaning that you can fill any combination of banks with memory, while RDRAM is a Parallel technology, which needs all banks filled either with memory modules or CRIMM's to keep the signal flowing from one end of the memory bus to the other.

RDRAM suffers from severe latencies, must be installed in pairs (the old 16-bit versions anyways) and are relatively expensive.

DDR SDRAM offers much better latencies, can be installed individually (only in single-channel mode though) and are relatively inexpensive.

That's how different these 2 memory technologies are.