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(double data rate synchronous dynamic random access memory) is a class
of memory integrated circuit used in computers. It achieves nearly twice
the bandwidth of the preceding [single data rate] SDRAM by double
pumping (transferring data on the rising and falling edges of the clock
signal) without increasing the clock frequency. 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As DDR-SDRAM is superseded by the newer DDR2 SDRAM, the older version
is sometimes referred to as DDR1-SDRAM.