Describes the physical interface portions of high performance electrical and optical link variants that support the higher level Fibre Channel protocols including FC-FS-2 and the higher Upper Level Protocols (ULPs) associated with HIPPI, SCSI, IP and others. This document contains all the requirements specified in FC-PI, FC-PI-2 and SM-LL-V that are recommended for new designs, plus requirements for 800 MB/s. FC-PI-4 does not replace FC-PI-2 but is intended to carry forward the technical requirements specified in FC-PI-2 for the variants addressed in FC-PI-4.