RDRAM

[cyberttc]

How fast does RDRAM runs?

 

[KarsinTheHutt]

In terms of bandwidth:

Per Channel:

PC800 ~ 1.6 GB/Sec
PC700 ~ 1.4 GB/Sec
PC600 ~ 1.2 GB/Sec

To put this in perspective...

PC100 ~ 0.8 GB/Sec
PC133 ~ 1.06 GB/Sec

However, I might add that Rambus has a higher latency, meaning that it takes the RDRAM interface longer to find information than it takes SDRAM.

 

[cyberttc]

So does PC800 runs at 800Mhz bus?

 

[yiwonder]

No, but I don't remember where the 800 comes from though.

 

[KarsinTheHutt]

well...

PC800 is really PC400 DDR. 400 MHz transfering data on each edge of a clock cycle.

However, the interface is only 16 bits wide, whereas an SDRAM interface is 64 bits wide.

Rambus = narrow, fast channel
Sdram = wider, slower channel

 

[GL]

Actually for RDRAM the PC number does indicate the "MHz" it runs at. For DDR SDRAM, the PC number doesn't indicate the "MHz" speed it runs at. However, the front side bus of the CPU that uses the RDRAM isn't that number. In the case of the Pentium 4, it is 100MHz quadruple-data rate which essentially is a 400MHz bus.

EDIT: OK don't listen to me I was wrong Like somebody mentioned, RDRAM is double data rate so divide the PC number in half and you'll get your actual operating speed.

-GL

 

[cyberttc]

P4 systems run at 400Mhz while using 800Mhz DDR ram speed?

 

[Finality]

Few things to note. i850 boards use dual channel so

a) you need to pair 2 sticks together
b) its effectively double the bandwidth of a single stick

But as we all know memory bandwidth for the P4 still does not make it a great processor.