Hey is Direct Rambus the same as DDR ram?

[gibear2000]

If not what is it?

 

[fkloster]

Close. For example PC-800 rdram is 400mhz double pumped up & down both sides. 16 bit data path. One could call rdram "double data rate". DDR sdram has a 64 bit data path. Rdram is serial memory. Sdram is parrallel.

 

[interchange]

Heeellll no....

Direct Rambus is the same as RDRAM, which is bad. Very bad. RDRAM, I'm sure you've heard of it (also Rambus DRAM, or just Rambus) is what the i820 uses for memory. It's incredibly expensive in comparison to SDRAM and DDR SDRAM. Moreover, it is debatably slower. RDRAM has a high latency associated with it, but the bandwidth provided is very impressive. Overall, this averages out.

Intel jumped on the Rambus bandwagon long ago, and they got screwed because they expected prices to go way down.

The next Athlon memory technology, however, is DDR SDRAM. This is the same stuff used in DDR Video cards. Basically, it transfers data at both the rising and falling edges of the clock = twice the bandwidth of normal SDRAM at the same latency. This rivals Rambus, and the performance gain is generally quite noticable.

Keep in mind that both RDRAM and DDR SDRAM are not useful when a small amount of data is being transferred at one time.

Edit:

Yeah, RAMBUS does do "double-pumping" or DDR, which makes PC800 RDRAM. But, generally, DDR RAM is considered SDRAM and not Rambus. Direct Rambus DRAM is a synonym for RDRAM, and does not imply DDR operation.

 

[Noriaki]

No they are not.
They both use both clock edges but that's the only similarity.

DDR is the next generation SDRAM, it uses a 64bit datapath and runs at 100 or 133Mhz using both clock edges (yeilding an effective 200 or 266Mhz clock).

Rambus is Rambus, it uses a 16bit datapath and runs at 266-400Mhz using both edges of the clock (yeilding an effective 533-800Mhz clock).

 

[Czar]

In a way they are the same, they use the same techinqe to double the bandwith.

 

[gibear2000]

Thanks very helpful. I saw a old AMD release were they licensed the Direct Rambus Technology for use with their new chipsets. here wonder what hap?

 

[fkloster]

Amd is smart. Why have all your eggs in one basket...

 

[Noriaki]

<< Thanks very helpful. I saw a old AMD release were they licensed the Direct Rambus Technology for use with their new chipsets. here wonder what hap? >>



AMD is driving DDR SDRAM right now, but why ignore Rambus?
They have a Rambus license so they can research and develop Rambus based chipsets, that way if Rambus becomes more mainstream they can pop out a Rambus based chipset.

Besides Rambus might perform really well with an Athlon.
A Pentium3 FSB is capable of 0.8 or 1GB/s bandwidth, matched perfectly by PC100 or PC133 SDRAM. More bandwidth on the RAM side gets chocked out by the FSB anyways.
An Athlon has a FSB speed of 1.6GB/s, which is the same as PC800 Rambus, it may be that it would perform quite well.

(Same story for the P4 if you are interested, it uses 3.2GB/s FSB Bandwidth, which is what Dual Channel PC800 Rambus is capable of)

Rambus may still prove to be a very valuable memory technology (I personally think the P3 was the wrong chip to debut it on) and AMD doesn't want to be left out in the cold if it is, they are simply being wise business men.

 

[fkloster]

Noriaki, very wise insight! Never thought of that.