USB, SPI, I²C, Sata - all these interfaces is common that they are serial interfaces. Serial interfaces are todays common. But why is that the case, especially for high-speed communication? it sounds simply counterintuitive: Parallel wires can theoretically send more bits per time than on singular wire can. The answer to that question is complex and multilayered. There are multiple different reasons why serial interfaces are preferred over parallel interfaces. Lets start with the obvious ones: The PCB routing of busses of 8, 16, 32 or even 64 bit width gets increasingly complex to route on printed circuits boards (PCBs).The second problem, related to this, is that signal slope need to get transmitted at the same time for all parallel lines (wires), which results in a more complex routing since edges in the strip conductor needs to be compensated. Simply put the additional logic implemented in chips to convert the serial signal to parallel ones again (deserializer) and vice versa (serializer) is much cheaper than the costs of complex routings.