Explanation of CIO and SIO

In the Features list of the RLDRAM II Controller Core, I read this:

• Up to 100 percent throughput possible for read or write requests (excluding refresh cycles) using common input/output (CIO) RLDRAM II devices

• Up to 100 percent simultaneous read and write throughput possible (excluding refresh cycles) using separated input/output (SIO) RLDRAM II devices

Can someone provide an explanation of what CIO and SIO mean here and how they are different (and how those differences mean to a designer)?