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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:
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 per cycle) may have a larger CAS latency of 9, but at a clock frequency of 1333 MHz the amount of time to wait 9 ...
A module of any particular size can therefore be assembled either from 32 small chips (36 for ECC memory), or 16(18) or 8(9) bigger ones. DDR memory bus width per channel is 64 bits (72 for ECC memory). Total module bit width is a product of bits per chip and number of chips. It also equals number of ranks (rows) multiplied by DDR memory bus width.
DDR SDRAM (sometimes called DDR1 for greater clarity) doubles the minimum read or write unit; every access refers to at least two consecutive words. Typical DDR SDRAM clock rates are 133, 166 and 200 MHz (7.5, 6, and 5 ns/cycle), generally described as DDR-266, DDR-333 and DDR-400 (3.75, 3, and 2.5 ns per beat).
Double data rate SDRAM (DDR SDRAM or DDR) was a later development of SDRAM, used in PC memory beginning in 2000. Subsequent versions are numbered sequentially (DDR2, DDR3, etc.). DDR SDRAM internally performs double-width accesses at the clock rate, and uses a double data rate interface to transfer one half on each clock edge. DDR2 and DDR3 ...
PC2-5300 DDR2 SO-DIMM (for notebooks) Comparison of memory modules for desktop PCs (DIMM) Comparison of memory modules for portable/mobile PCs (SO-DIMM) The key difference between DDR2 and DDR SDRAM is the increase in prefetch length.
Thus with a memory clock frequency of 100 MHz, DDR3 SDRAM gives a maximum transfer rate of 6400 MB/s. The data rate (in MT/s) is twice the I/O bus clock (in MHz) due to the double data rate of DDR memory. As explained above, the bandwidth in MB/s is the data rate multiplied by eight.
The nomenclature differs across memory technologies, but for commodity DDR SDRAM, DDR2 SDRAM, and DDR3 SDRAM memory, the total bandwidth is the product of: Base DRAM clock frequency; Number of data transfers per clock: Two, in the case of "double data rate" (DDR, DDR2, DDR3, DDR4) memory.
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