DDR SDRAM is a future step in the development of a usual SDRAM. A technology Double Data Rate (DDR) enables to use the front and back fronts of clock pulse for information exchange. This increases twice the amount of transmitted information. Thus, an effective frequency of memory bus exceeds twice a frequency of operating bus.
General recommendations for choosing DDR SDRAM is similar to those for SDRAM as there is no fundamental difference between SDRAM and DDR SDRAM.
Nowadays the following modules of memory can be used: PC1600 – 100 MHz, PC2100 – 266 MHz and PC2700 – 333 MHz.
The CL latency time for such modules may have the values 3, 2.5 and 2.