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DDR2 DIMMs are neither forward compatible with DDR3 nor backward compatible with DDR. 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 ...
Each word will then be transmitted on consecutive rising and falling edges of the clock cycle. Similarly, in DDR2 with a 4n pre-fetch buffer, four consecutive data words are read and placed in buffer while a clock, which is twice faster than the internal clock of DDR, transmits each of the word in consecutive rising and falling edge of the ...
DDR2 picks up where DDR1 leaves off, utilizing internal clock rates similar to DDR1, but is available at effective transfer rates of 400 MHz and higher. DDR3 advances extended the ability to preserve internal clock rates while providing higher effective transfer rates by again doubling the prefetch depth.
Without knowing the clock frequency it is impossible to state if one set of timings is "faster" than another. For example, DDR3-2000 memory has a 1000 MHz clock frequency, which yields a 1 ns clock cycle. With this 1 ns clock, a CAS latency of 7 gives an absolute CAS latency of 7 ns. Faster DDR3-2666 memory (with a 1333 MHz clock, or 0.75 ns ...
DDR2 and DDR3 increased this factor to 4× and 8×, respectively, delivering 4-word and 8-word bursts over 2 and 4 clock cycles, respectively. The internal access rate is mostly unchanged (200 million per second for DDR-400, DDR2-800 and DDR3-1600 memory), but each access transfers more data.
Column address strobe latency, also called CAS latency or CL, is the delay in clock cycles between the READ command and the moment data is available. [1] [2] In asynchronous DRAM, the interval is specified in nanoseconds (absolute time). [3]
The DDR2 RAM that it is compatible with is known to be double-pumped and to have an Input/Output Bus twice that of the true FSB frequency (effectively transferring data 4 times a clock cycle), so to run the system synchronously (see front-side bus) the type of RAM that is appropriate is quadruple 266 MHz, or DDR2-1066 (PC2-8400 or PC2-8500 ...
Notch positions on DDR (top) and DDR2 (bottom) DIMM modules. On the bottom edge of 168-pin DIMMs there are two notches, and the location of each notch determines a particular feature of the module. The first notch is the DRAM key position, which represents RFU (reserved future use), registered , and unbuffered DIMM types (left, middle and right ...