RDram and DDR

[quaere]

CAn someone tell mi what is the difference between DDR and RDram. Which is better?😕

 

[dullard]

Welcome to Anandtech.

They are completely different technologies (I cannot explain the physical differences very well, but I'm sure other people here can) - thus it is difficult to say one is better than the other. Current DDR has lower latencies than current RDRAM. That means that the very first chunk of data is slightly faster with DDR (but all the rest of the data is unaffected). Current RDRAM has a larger bandwidth than current DDR. Thus RDRAM sends more information in a given amount of time than DDR does. They each have an advantage and a disadvantage.

One good comparison is to look at the new P4 motherboards. Most reviews show that a P4 runs about 3% faster using RDRAM than when it uses DDR. This is such a small difference that you will not be able to notice it.

DDR currently can overclock better than RDRAM, but this will change when the new PC1066 RDRAM comes out. So if you want to overclock, I'd go with DDR.

DDR is often a little cheaper than RDRAM, but the price difference is too small for most people to worry about. In fact, Dell often sells its P4 computer with RDRAM for $1 less than the DDR version.

 

[xxsk8er101xx]

RDRAM is ram from Rambus. With a single stick of pc800 (or 400mhz) it runs at 1600 megabytes per second. With Dual Channel architecture, meaning you need two sticks, it doubles the bandwidth to 3200 megabytes per second. 400mhz * 2^2 * 2^10 = 1638400 bytes per second. Now rdram is 16bit, and thats 2 bytes. and you multiply it by 2^10 to get the number of bytes. you do 2^(some number) to get the number of bits.

DDR is the evolution from sdram. It simply double pumps the data. Sdram runs at 133mhz for pc133. At 64bits or 8 bytes thats: 133mhz * 2^3 * 2^10 = 1089536. So essentially you can call it pc1100. Now ddr double pumps it so it's effective megahurts is 266mhz: 266mhz * 2^3 * 2^10 = 2179072. Thats your pc2100.

So as you can see DDR is better. DDR also has less latency then rdram. Now because rdram uses a dual channel architecture it's effective bandwidth is 1638400 * 2 = 3276800. Thats rdram with it's dual channel architecture.

The only chipset that uses dual channel ddr is the nforce. That is strictly for AMD as far as i know and AMD doesn't make use to the extra bandwidth it has so it's useless. If there was dual channel DDR for the pentium 4 the effective bandwidth would be 2179072 * 2 = 4358144.

Maybe thats more then you wanted to know just kind of recalling things for self learning reasons i guess you can call it.

I hope i answered your question 🙂

good luck!