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.
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 |
Voltage |
|
DDR |
256Mb – 1Gb | X4 – x16 | 167 MHz – 200 MHz | 2.5V, 2.6V |
|
DDR2 |
256Mb – 4Gb | x4 – x16 | 333MHz – 533 MHz | 1.8V |
|
DDR3 |
1Gb – 8Gb | X4 – x16x | 800 MHz – 1066 MHz | 1.35V, 1.5V |
|
DDR4 |
4Gb – 32 Gb | X4 – 16x | 1200 MHz – 1866 MHz | 1.2V |
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