This post covers topic of DDR SDRAM double data rate memory. DDR (Double Data Rate) SDRAM memory is a memory type that provides direct path to double memory bandwidth, due to data access on the both raising and falling edges of the clock signal. It makes DDR memory incompatible with classic SDRAM controller, and requires it’s own DDR controller. 

The figure below shows principal comparison of SDR and DDR SDRAM double data rate memory.

SDR and DDR comparison
SDR and DDR comparison

The size of refetch of DDR SDRAM is 2, it means that at each access fetch results in two data words.

DDR memory types now have several types in accordance to the technology development : DDR, DDR2, DDR3, DDR4.

Memory type

Density Width Clock rate



256Mb – 1Gb X4 – x16 167 MHz – 200 MHz 2.5V, 2.6V


256Mb – 4Gb x4 – x16 333MHz – 533 MHz 1.8V


1Gb – 8Gb X4 – x16x 800 MHz – 1066 MHz 1.35V, 1.5V


4Gb – 32 Gb X4 – 16x 1200 MHz – 1866 MHz 1.2V

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