Software-defined data centers have not yet become realities. But the idea of a software-defined data center took flight in 2013. Software-defined refers to the abstraction of the functionality of some traditional data center hardware component such as a networking switch or storage array into software, adding some type of orchestration and automation and making it available to applications via APIs -- either open source or proprietary -- to let those applications better control the functionality.
In 2013, nearly every storage and networking vendor either introduced, or said they did, software-defined technology or said their products are ready for it. Startups by the dozens also came to market with software-defined-focused technology.
What's left to be done? Getting everyone to agree on a definition and standards and then following through on those agreements. And that is much more difficult than pledging support for the technology.