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DDR SDRAM specification was finalized by JEDEC in June 2000 (JESD79). [9] JEDEC has set standards for the data rates of DDR SDRAM, divided into two parts. The first specification is for memory chips, and the second is for memory modules. The first retail PC motherboard using DDR SDRAM was released in August 2000. [10]
DDR4 speeds are advertised as double the base clock rate due to its Double Data Rate (DDR) nature, with common speeds including DDR4-2400 and DDR4-3200, and higher speeds like DDR4-4266 and DDR4-5000 available at a premium. Unlike DDR3, DDR4 does not have a low voltage variant; it consistently operates at 1.2 V. Additionally, DDR4 improves on ...
In contrast, the prefetch buffer of DDR2 is 4-burst-deep, and the prefetch buffer of DDR is 2-burst-deep. This advantage is an enabling technology in DDR3's transfer speed. DDR3 modules can transfer data at a rate of 800–2133 MT/s using both rising and falling edges of a 400–1066 MHz I/O clock. This is twice DDR2's data transfer rates (400 ...
DDR SDRAM (sometimes called DDR1 for greater clarity) doubles the minimum read or write unit; every access refers to at least two consecutive words. Typical DDR SDRAM clock rates are 133, 166 and 200 MHz (7.5, 6, and 5 ns/cycle), generally described as DDR-266, DDR-333 and DDR-400 (3.75, 3, and 2.5 ns per beat).
DDR SDRAM operating with a 100 MHz clock is called DDR-200 (after its 200 MT/s data transfer rate), and a 64-bit (8-byte) wide DIMM operated at that data rate is called PC-1600, after its 1600 MB/s peak (theoretical) bandwidth. Likewise, 12.8 GB/s transfer rate DDR3-1600 is called PC3-12800. Some examples of popular designations of DDR modules:
In addition to double pumping the data bus as in DDR SDRAM (transferring data on the rising and falling edges of the bus clock signal), DDR2 allows higher bus speed and requires lower power by running the internal clock at half the speed of the data bus. The two factors combine to produce a total of four data transfers per internal clock cycle.
What determines absolute latency (and thus system performance) is determined by both the timings and the memory clock frequency. When translating memory timings into actual latency, it is important to note that timings are in units of clock cycles, which for double data rate memory is half the speed of the commonly quoted transfer rate. Without ...
Standard DDR5 memory speeds range from 4,000 to 6,400 million transfers per second (PC5-32000 to PC5-51200). [3] Higher speeds may be added later, as happened with previous generations. Compared to DDR4 SDRAM, the minimum burst length was doubled to 16, with the option of "burst chop" after eight transfers.