By: Robert Halford, July 8, 2003 Print this article
Many find the difference between FSB, DDR, RAMBUS and how it works quite confusing, so in this short write-up, I'll try to explain the difference. Enjoy.
DDR transfer data on both rising and falling edge, and this applies for any system using DDR whether it's AMD or Intel. If your DDR ram is rated as 266MHz DDR, then it's physically running at 133, but as it transfers data twice on the same clock pulse, it's "virtually running at" 266.
As with RAMBUS, it's quad pumped using both the DDR technique of transfering on rising and falling edge as well as being phaseshifted. The result is four times data throughput. RDRAM running at 400MHz is physically running at 100MHz(4x100=400). 533MHz/4=133MHz physical FSB.
FSB and other busses
The CPU speed depends on two factors: The multiplier and FrontSideBus, and as the multiplier on all P4 are locked, you can only change the FSB.
Increasing the FSB also increases the AGP, PCI and all other ports using the FSB as reference frequency. Some P4 motherboards, however, let you fix the AGP and PCI speed regardless of what your FSB is, and they may also let you set a different RAM speed than what your FSB is.
Hope I've cleared up a few things.