A data processing system and method of isolating a plurality of I/O adapters in the system. The data processing system also comprises a set of processors communicating with the I/O adapters using a PCIe protocol. Each of the I/O adapters has a respective ID. In the preferred embodiment the commands issued by the I/O adapters include a PCIe defined Requestor ID field including one or more of the Requestor IDs of I/O Adapters. The Req IDs can be used as an input to a CAM which provides an index to a TVT to identify a unique and independent system memory space for the I/O adapter.