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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 ...
DDR5 has about the same 14 ns latency as DDR4 and DDR3. [7] DDR5 octuples the maximum DIMM capacity from 64 GB to 512 GB. [8] [3] DDR5 also has higher frequencies than DDR4, up to 8GT/s which translates into 64 GB/s (8 gigatransfers/second × 64-bits/module / 8 bits/byte = 64 GB/s) of bandwidth per DIMM.
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]
At higher clock rates, the useful CAS latency in clock cycles naturally increases. 10–15 ns is 2–3 cycles (CL2–3) of the 200 MHz clock of DDR-400 SDRAM, CL4-6 for DDR2-800, and CL8-12 for DDR3-1600. Slower clock cycles will naturally allow lower numbers of CAS latency cycles.
Address and control signals are still sent to the DRAM once per clock cycle (to be precise, on the rising edge of the clock), and timing parameters such as CAS latency are specified in clock cycles. Some less common DRAM interfaces, notably LPDDR2 , GDDR5 and XDR DRAM , send commands and addresses using double data rate.
The GDDR5 interface transfers two 32-bit wide data words per write clock (WCK) cycle to/from the I/O pins. Corresponding to the 8N-prefetch, a single write or read access consists of a 256-bit wide two CK clock cycle data transfer at the internal memory core and eight corresponding 32-bit wide one-half WCK clock cycle data transfers at the I/O ...
Because the CAS latency is specified in clock cycles, and not transfers (which occur on both the rising and falling edges of the clock), it is important to ensure it is the clock rate (half of the transfer rate) which is being used to compute CAS latency times. [citation needed] Another complicating factor is the use of burst transfers.
One 64 GiB DDR5-4800 ECC 1.1 V registered DIMM (RDIMM) Example of an unregistered DIMM (UDIMM) Registered memory (also called buffered memory) is computer memory that has a register between the DRAM modules and the system's memory controller. A registered memory module places less electrical load on a memory controller than an unregistered one.