This primer is devoted to the topic of validating a digital “system”&#151an individual transceiver set used in applications such as exchanging data between a motherboard-mounted chipset and a hard disk drive. It will concentrate on the analysis of the basic building blocks in serial bus architectures such as Serial ATA, 10 Gigabit Ethernet, XAUI and others. This small system is a complete transmit/receive interface consisting of a transmitter device with differential outputs, a transmission link, typically made up of circuit board traces, interconnecting cables, and connectors, and finally a receiver device, that is also differential.