This specification describes the extensions required to allow PCI Express Devices to interact with an address translation agent (TA) in or above a Root Complex (RC) to enable translations of DMA addresses to be cached in the Device. The purpose of having an Address Translation Cache (ATC) in a Device is to minimize latency and to provide a scalable distributed caching solution that will improve I/O performance while alleviating TA resource pressure. This specification must be used in conjunction with the PCI Express Base Specification, Revision 1.1, and associated ECNs.