In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a DTE such as a computer terminal or PC, and a DCE, such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. The RS-232 standard had been commonly used in computer serial ports and is still widely used in industrial communication devices.
PCI Express x1 card with one RS-232 port on a nine-pin connector
USRobotics Courier external modem had a DB-25 connector that used the Ring Indicator signal to notify the host computer when the connected telephone line was ringing
A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and predated the use of a computer screen by decades. Starting in the mid-1970s with machines such as the Sphere 1, Sol-20, and Apple I, terminal circuitry began to be integrated into personal and workstation computer systems, with the computer handling character generation and outputting to a CRT display such as a computer monitor or, sometimes, a consumer TV.
A Teletype Model 33 ASR teleprinter, usable as a terminal
Closeup of an IBM 2741 printing terminal, which used a changeable Selectric "golfball" typing element and was faster than the earlier teletype machines
IBM 2260
ADM-3A