DDR2 PCB design: get it right the first time

What is DDR2?
Acronym for Double-Data-Rate Two, which refers to a computer memory technology as it applies to synchronous dynamic random access memory (SDRAM). Standards are defined for the ICs as well as the DIMMs they enable. A single-data-rate SDRAM transfers data on every rising edge of the clock pulse 100MHz. Both DDR and DDR2 are double pumped—they transfer data on the rising and falling edges of the clock, achieving an effective rate of 200MHz with the same clock frequency. The difference between DDR2 to DDR is a doubled bus frequency for the same physical clock rate, which doubles the data rate yet another time.