DDR3 SDRAM Memory

- overview, tutorial about the basics of what is DDR3 SDRAM, its technology operation, advantages & disadvantages.

DDR3 is the third generation of DDR SDRAM technology.

DDR3 SDRAM brings with it further improvements in overall performance and as a result its use is more widespread.

The DDR3 SDRAM technology provides data speeds of 800 Mbps, the highest speed for DDR2 SDRAM.


DDR3 SDRAM basics

The DDR3 SDRAM memories provide a number of improvements over the previous generation of SDRAM memories:

  • Higher data rate:   The DDR3 SDRAM provides data rates starting at 800Mbps per pin using a clock rate of 400 MHz.

    DDR3 SDRAM Type Data Rate
    Mb/s/pin
    Memory Clock Speed
    (MHz)
    DDR3-800
    800
    400
    DDR3-1066
    1066
    533
    DDR3-1333
    1333
    667
    DDR3-1600
    1600
    800
    DDR3-1866
    1866
    933
    DDR3-2133
    2133
    1066
  • Reduce supply voltage:   The supply voltage is reduced to 1.5 volts compared to the 1.8 volts used for the previous generation.
  • Lower power consumption:   the reduction in power supply voltage alone reduces the power consumed by equivalent chips (if they were available) by a factor of 0.69.
  • DQ line impedance:   The DQ line driver impedance is higher at 34 Ω than the previous generation which were only 18 Ω.
  • Memory capability:   The memory size of the DDR3 SDRAM chips started at 512 Mb and grew to 8 Gb.
  • Prefetch buffer:   The pre-fetch buffer in the DDR3 technology has been increased to 8 bits thereby increasing their speed of operation. DDR3 SDRAM uses an 8n prefetch architecture and this enables 8 data words to be transferred in 4 clock cycles.
  • Memory configurations:   DDR3 SDRAM includes x4, x8, and x16 data output configurations as in previous generations, but DDR3 SDRAM has eight banks whereas DDR2 had either four or eight dependent upon the size of the memory.
  • Mode registers:   DDR3 SDRAM has four mode registers. DDR2 had the same number, but only two were used as the others were reserved for future use. DDR3 uses all four registers, and they have settings for CAS read latency and the write latency.
  • On-Die Termination, ODT:   Like DDR2, DDR3 SDRAM uses ODT which enables the correct terminations to be applied on the chip itself. The technology was introduced on DDR2, (DDR used termination on the motherboard which limited the speeds attainable). With speeds of the
  • Packages and pins:   DDR3 SDRAMs all use surface mount BGA, Ball Grid Array, style integrated circuit packages. DDR2 also use BGAs, but the much older DDR SDRAMs use almost always use TSOP, Thin Small-Outline Package, packaging, although there are a few DDR chips that use BGA packages.

    The number of pins on a DDR3 memory module is 240. This is the same as DDR2.

    Memory Module Number of Pins
    DDR
    184
    DDR2
    240 *
    DDR3
    240 *
    * Even though the DDR2 and DDR3 memory modules have the same number of pins, they are not interchangeable because the notch or key is in a different position. This is because they are also not electrically interchangeable. Some motherboards do allow for both types, but these are designed to accept both and cater for the electrical differences.

By Ian Poole


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