As we said some months ago, AMD integrated a dual IMC (DDR3 and DDR4) in Carrizo and Toronto, but the DDR4 IMC is disabled in Carrizo. The same die will be used in the consumer market (Carrizo) and in the enterprise market (Toronto), because AMD have to optimize the production.
This choice was made because the price of DDR4 memory will remain high till 2016, according to Intel sources, so the DDR3 memory will remain the leader in this market for a long time. The only real advantage of the DDR4 over the DDR3 is about the lower power consumption, but it's a useless advantage if we consider that in the high-density server market the LPDDR4 will dethrone the classical DDR4 chips.
Even Intel, for the first time, has taken a similar decision with SkyLake integrating a dual DDR3/DDR4 IMC, to promote its own new platform.
However, in the near future, AMD could commercialize a new Carrizo revision with the DDR4 IMC enabled, if the DDR4 memory will be cheaper (on the other hand, the GDRR5 IMC of Kaveri will never be enabled). Toronto will have the both IMC enabled from the beginning.
