Standard RS-232, respectively its last version RS-232C dating back to 1969 (also referred to as the serial port or serial line) is used as a communication interface for personal computers and other electronics. The individual data bits are transmitted sequentially (in series); one pair of wires is used in each direction. Unlike network technology (e.g. Ethernet) or USB interface, RS-232 is completely collision-free physical layer.
Since 2010, RS232 has been replaced in most personal computers by a universal serial bus (USB). Modifications of RS-232 (standard RS-422 and RS‑485) are used very often in the industry because of their specific features and it is certain that in near future they will not be replaced. In the reference model ISO/OSI, the RS-232 bus is represented only by the physical layer. The usual transfer rates are 115 200; 57600; 38400; 19200; 9600; 4800; 2400; 1200; 600; 300 bit/s. Actual (effective) speed is always lower, because to each of the 8 data bits transmitted, additional 1 start bit, 1 or 2 stop bits and also the parity bit are attached. Typical distance from device to device connected over RS-232 is 15 m depending on the capacity of cables; up to 300 m can be reached with low-capacity cables.