|
DDR has its name because it can output data twice faster than SDRAM of the same frequency. That is, twice per clock cycle, on the signal’s rising and falling edges. But these data should be taken from somewhere, yes? The developers went for a trick: the memory cells are working at the same frequency, but the internal bus is wider to boost the data-transfer rate inside the chip.The key principle of DDR2 is easy to understand once you learn what DDR SDRAM is. Like with DDR, the internal bank issues data to the I/O buffers along a broad 64-bit 100MHz internal bus. But now the data go from the buffer at a faster and narrower bus (16 bit, 200MHz), which uses the Double Data Rate trick. Thus, we achieve a resulting data-rate frequency of 400MHz.
Source:X-bitlabs
|