DDR SDRAM
Key Properties
- 2-bit pre-fetch
- SSTL-2, source synchronous interface
- 200~400MHz per Pin
DDR SDRAM or
Double-Data-Rate
synchronous dynamic random access memory is a type of memory integrated
circuit used in computers. It achieves greater bandwidth than ordinary
SDRAM by transferring data on both the rising and falling edges of the
clock signal (double pumped). This effectively nearly doubles the transfer
rate without increasing the frequency of the front side bus. Thus a 100 MHz
DDR system has an effective clock rate of 200 MHz when compared to
equivalent SDR SDRAM, the “SDR” being a retrospective designation.
With data being transferred 8 bytes at
a time DDR RAM gives a transfer rate of (memory bus clock rate) × 2 (for
dual rate) × 8 (number of bytes transferred). Thus with a bus frequency of
100 MHz, DDR-SDRAM gives a max transfer rate of 1600 MB/s.
JEDEC has set standards for speeds of
DDR SDRAM, divided into two parts: The first specification is for memory
chips and the second is for memory modules.
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