DDR reads data at both the rising and falling edges of the clock tick, and is twice as fast as SDRAM. This may be referred to, as transferring data at half a cycle.
Common DDR speeds are 200, 266, 333 and 400 MHz.
Identification – speed in MHz times 8 (width of a DDR SDRAM) i.e. 200 MHz times 8 = 1600 thus PC 1600
184-pin DDR DIMM (PC1600, PC2100 & PC2700)
PC100 SDRAM modules are rated at 8 ns at 100 MHz
PC133 SDRAM modules are rated at 12 ns at 133 MHz.
