SDR SDRAM is Single Data Rate SDRAM.

SDR SDRAM is the original SDRAM standard, which has since been replaced by DDR SDRAM.

DDR SDRAM doubles the bandwidth of SDR DRAM by transferring data twice per cycle on both edges of the clock signal, implementing burst mode data transfer.

Standard SDR SDRAM DIMMs

SDR SDRAM is normally packaged in DIMM modules.

SDRAM DIMM modules are sold according to clock speed (MHz), bus speed (megatransfers per second), and transfer rate (megabytes per second.

DIMM Module Chip Type Clock Speed Bus Speed Transfer Rate
PC66 10ns 66 66 533
PC100 8ns 100 100 800
PC133 7.5/7ns 133 133 1,066

SDR SDRAM