What is DDR SDRAM?

DDR SDRAM is Double Data Rate SDRAM.

DDR SDRAM is an improvement over regular SDRAM, also known as SDR SDRAM (Single Data Rate 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.

DDR SDRAM is being supplanted by DDR2 SDRAM.

Standard DDR SDRAM DIMM's

DDR SDRAM is normally packaged in DIMM modules.

DIMM Module	Chip Type	Clock Speed	Data Rate	Transfer Rate
PC1600	DDR200	100	200	1,600
PC2100	DDR266	133	266	2,133
PC2400	DDR300	150	300	2,400
PC2700	DDR333	166	333	2,667
PC3000	DDR366	183	366	2,933
PC3200	DDR400	200	400	3,200
PC3500	DDR433	216	433	3,466
PC3700	DDR466	233	466	3,733
PC4000	DDR500	250	500	4,000
PC4300	DDR533	266	533	4,266

Standards for DDR SDRAM

DDR SDRAM standards are still being developed and improved.

DDR SDRAM Standard	Frequency (MHz)	Voltage
DDR	400-533	2.5
DDR2	667-800	1.8
DDR3	1066 to ...	1.5

Higher frequencies enable higher rates of data transfer.

Lower voltages result in less heat radiation and longer batter life for portable computing devices. They also allow greater component density, which allows higher capacity in the same package size.