Historically, users accessed a UNIX system using a terminal connected via a serial line (an RS-232 connection). Terminals were cathode ray tubes (CRTs) capable of displaying characters and, in some cases, primitive graphics. Typically, CRTs provided a monochrome display of 24 lines by 80 columns. By today’s standards, these CRTs were small and expensive. In even earlier times, terminals were sometimes hard-copy teletype devices. Serial lines were also used to connect other devices, such as printers and modems, to a computer or to connect one computer to another.
On early UNIX systems, the terminal lines connected to the system were represented
by character devices with names of the form
/dev/ttyn. (On Linux, the /