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DDR3-2000 memory with 9-9-9-28 latency (9 ns) was available in time to coincide with the Intel Core i7 release in late 2008, [19] while later developments made DDR3-2400 widely available (with CL 9–12 cycles = 7.5–10 ns), and speeds up to DDR3-3200 available (with CL 13 cycles = 8.125 ns).
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.
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 ...
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.
The DDR4 SDRAM is a high-speed dynamic random-access memory internally configured as 16 banks, 4 bank groups with 4 banks for each bank group for ×4/×8 and 8 banks, 2 bank groups with 4 banks for each bank group for ×16 DRAM. The DDR4 SDRAM uses an 8n prefetch architecture to achieve high-speed
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.
At the 2007 Intel Developer Forum, it was revealed that major memory manufacturers have no plans to extend FB-DIMM to support DDR3 SDRAM. Instead, only registered DIMM for DDR3 SDRAM had been demonstrated. [15] In 2007, Intel demonstrated FB-DIMM with shorter latencies, CL5 and CL3, showing improvement in latencies. [16]
The standards specify the physical and electrical characteristics of the modules, and include the data for computer simulations of the memory module operating in a system. [10] Memory modules of the DDR2-SDRAM type are available for laptop, desktop, and server computers in a wide selection of capacities and access speeds.