Over the years, as applications have become more demanding, systems
have increasingly resorted to external memory as a way to boost
performance while reducing cost. Single data rate (SDR) memories gave
way to double data rate (DDR) memories as system designers continually
sought solutions to boost system performance without increasing system
complexity and cost.
DDR2 SDRAM is the next generation of DDR SDRAM technology, with
improvements that include lower power consumption, higher data
bandwidth, enhanced signal quality, and on-die termination schemes.
DDR2 SDRAM brings higher memory performance to a broad range of
applications, such as PCs, embedded processor systems, image
processing, storage, communications, and networking.
DDR SDRAM is currently the popular memory of choice. Designers
looking to save system power are moving toward using DDR2 SDRAM,
which uses a lower 1.8-V I/O voltage compared to the DDR SDRAM I/O
voltage of 2.5 V. Table 1 shows the DDR and DDR2 SDRAM interface
support in Cyclone? II devices.