Despite the increasing popularity of USB, serial communications remain important to many PC users. PCs use serial communications to connect peripherals such as mice, modems, PDA cradles, barcode readers, and similar low-speed devices. In one sense, serial communications are straightforward. If you use the right cable and let Windows or Linux take care of configuring parameters, everything usually just works. When it doesn't, however, you need to understand quite a bit about the underlying plumbing to make things right. This chapter describes what you need to know about PC serial communications.