RS-232C Recommended Standard-232C
Developed by the EIA sequence (SERIAL) signal interfaces, PC's SERIAL PORT otherwise known as COM1 and COM2 interface is RS-232C.

RS-422 Recommended Standard-422
Developed by the EIA sequence (SERIAL) signal interface supporting transfer rate than the RS-232 fast. RS-423 similar to the RS-422, but only to support Point to Point (POINT-TO-POINT) communications.

RS-423 Recommended Standard-423
Developed by the EIA sequence (SERIAL) signal interface supporting transfer rate than the RS-232 fast. RS-422 similar to the RS-423, but the support for multi-point (MULTIPOINT) communications.

RS-485 Recommended Standard-485
Developed by the EIA sequence (SERIAL) signal interface, similar to RS-422, but each line can have more nodes (NODE).

RS232 CommunicationRS-232 was first introduced in 1962.[2] The original DTEs were electromechanical teletypewriters and the original DCEs were (usually) modems. When electronic terminals (smart and dumb) began to be used, they were often designed to be interchangeable with teletypes, and so supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices.