Now in its fourth generation, which sports data-transfer rates up to 16 Gb/s, Peripheral Component Interface Express standard (PCI Express, or PCIe) requires challenging physical-layer test requirements (Figure 1). We've covered electrical compliance test for PCIe 3.0 in some detail, but with the test specifications for PCIe 4.0 rounding into shape, it's time for a deep dive into electrical compliance test for this ubiquitous peripheral interface protocol.