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Double Data Rate 4 Synchronous Dynamic Random-Access Memory (DDR4 SDRAM) is a type of synchronous dynamic random-access memory with a high bandwidth ("double data rate") interface. Released to the market in 2014, [ 2 ] [ 3 ] [ 4 ] it is a variant of dynamic random-access memory (DRAM), some of which have been in use since the early 1970s, [ 5 ...
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, timings are in units of clock cycles, which for double data rate memory is half the speed of the commonly quoted transfer rate. Without knowing the clock frequency ...
The figures below are simplex data rates, which may conflict with the duplex rates vendors sometimes use in promotional materials. Where two values are listed, the first value is the downstream rate and the second value is the upstream rate. The use of decimal prefixes is standard in data communications.
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. Latency is therefore a fundamental measure of the speed ...
For a completely unknown memory access (AKA Random access), the relevant latency is the time to close any open row, plus the time to open the desired row, followed by the CAS latency to read data from it. Due to spatial locality, however, it is common to access several words in the same row. In this case, the CAS latency alone determines the ...
The 8n prefetch architecture is combined with an interface designed to transfer two data words per clock cycle at the I/O pins. A single read or write operation for the DDR4 SDRAM consists of a single 8n-bit-wide 4-clock data transfer at the internal DRAM core and 8 corresponding n-bit-wide half-clock-cycle data transfers at the I/O pins. [20]
Memory bandwidth is the rate at which data can be read from or stored into a semiconductor memory by a processor.Memory bandwidth is usually expressed in units of bytes/second, though this can vary for systems with natural data sizes that are not a multiple of the commonly used 8-bit bytes.
DDR3 and DDR4 use A12 during read and write command to indicate "burst chop", half-length data transfer; DDR4 changes the encoding of the activate command. A new signal ACT controls it, during which the other control lines are used as row address bits 16, 15 and 14. When ACT is high, other commands are the same as above.