These represent the 3 different iPass versions that were adopted into the PCI Express (PCIe) External Cable Spec, released in January 2007. The x4 standard specifies a 36 circuit SMT host connector, a die cast EMI guide frame, available in single (1x1), dual (1x2) or quad (1x4) versions, and a shielded plug cable assembly. The x8 standard specifies a 68 circuit SMT host connector, a die cast EMI guide frame, and a shielded plug cable assembly. The x16 standard is more unique. It specifies a 136 circuit press-fit connector assembly, which includes an integral guide frame and a shielded plug cable assembly. Also unique to the x16 is that it alone has a dual paddle-card interface. The x4 and x8 PCIe, along with the Mini-SAS/Mini-SATA standards specify a single paddle card. Similar to SFF-8088 external Mini-SAS/Mini-SATA, the PCIe standard uses GREEN color-coding and separate, unique keying positions.