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DDR SDRAM or double data rate synchronous dynamic random access memory is a class of memory integrated circuit used in computers. It achieves greater bandwidth than the preceding single data rate SDRAM by transferring data on the rising and falling edges of the clock signal (double pumped). Effectively, it doubles the transfer rate without increasing the frequency of the memory bus.
With data being transferred 64 bits at a time, DDR SDRAM gives a transfer rate of (memory bus clock rate) ?2 (for dual rate) ?64 (number of bits transferred) / 8 (number of bits/byte). Thus with a bus frequency of 100 MHz, DDR-SDRAM gives a maximum 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.
As DDR is superseded by the newer DDR2, the older version is commonly referred to as DDR1.
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