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It is the higher-speed successor to DDR and DDR2 and predecessor to DDR4 synchronous dynamic random-access memory (SDRAM) chips. DDR3 SDRAM is neither forward nor backward compatible with any earlier type of random-access memory (RAM) because of different signaling voltages, timings, and other factors. DDR3 is a DRAM interface specification.
It is for this reason that DDR3-2666 CL9 has a smaller absolute CAS latency than DDR3-2000 CL7 memory. Both for DDR3 and DDR4, the four timings described earlier are not the only relevant timings and give a very short overview of the performance of memory. The full memory timings of a memory module are stored inside of a module's SPD chip.
Memory latency is the time (the latency) between initiating a request for a byte or word in memory until it is retrieved by a processor. If the data are not in the processor's cache , it takes longer to obtain them, as the processor will have to communicate with the external memory cells.
As with all DDR SDRAM generations, commands are still restricted to one clock edge and command latencies are given in terms of clock cycles, which are half the speed of the usually quoted transfer rate (a CAS latency of 8 with DDR3-800 is 8/(400 MHz) = 20 ns, exactly the same latency of CAS2 on PC100 SDR SDRAM). DDR3 memory chips are being made ...
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]
The CAS latency is the delay between the time at which the column address and the column address strobe signal are presented to the memory module and the time at which the corresponding data is made available by the memory module. The desired row must already be active; if it is not, additional time is required.
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:
GDDR3 SDRAM (Graphics Double Data Rate 3 SDRAM) is a type of DDR SDRAM specialized for graphics processing units (GPUs) offering less access latency and greater device bandwidths. [ compared to? ] Its specification was developed by ATI Technologies in collaboration with DRAM vendors including Elpida Memory , Hynix Semiconductor , Infineon ...