Yes, Opterons, and Athlon 64 FX's support 128bit DDR (Which is both Dual DDR and 128bit combined)
A little explination of the differenced between 64-bit, 128-bit and Dual DDR
With 64-Bit DDR a processor can grab up to 64-bits of data per clock over the memory bus.
If you have two dimms on your bus, latency can become an issue as it can take up to 6 extra clock cycles to change from reading Dimm 0, to reading from Dimm 1
Dual DDR reduced latency on the bus by seperating the dimms onto two seperate 64-bit Busses. This means during the 3clock cycles (CAS3) while Dimm 0 is in executing a command, the memory controller can take that time and issue a command to Dimm1, then flip-flop between the two reading and writing to each Bus in turn, but with less latency.
On a Athlon XP the bus to the processor is only 64-bits wide, so a Dual DDR setup has to flip-flop between dimms tranfering 64bits at a dim.
128-bit DDR can work like Dual DDR, writing two interlaced sets of 64-bit data.
(By flip-floping which dimm to write or read from)
But 128-bit DDR also can reach out and grab data from both dimms at the same time if needed.
This is possible on a Athlon FX, or Opteron
The memory contoller can handle a full 128bits per clock cycle rather then two sets of 64bits per 2 clocks.
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