RS-232 Connectors
The Electronic Industries Association (EIA) RS-232 specification, specifies pin-outs on a 25 pin subminiature D series connector, a DB-25. When the PC was introduced the RS-232 serial communications port was implemented on a 9 pin subminiature D series connector, a DE-9.
The interface is a single ended interface and as such is only useful for short distances of 50 feet or less. The maximum length depends on the baud rate and the type of cable used.
Data Communications Equipment (DCE)
Data Communication Equipment is any equipment to be used to facilitate the exchange of data. This typically includes Modems and other such like equipment.
Data Terminal Equipment (DTE)
Data Terminal Equipment is any type of used at the end of the communication link. This typically includes Computer Terminals, Personal Computers (PC), Printers and other such like equipment.