RS-232 An RS - 232 serial port was once a standard feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies, and other peripheral devices. RS -232C RS-232 stands for Recommend Standard number 232 and C is the latest revision of the standard. The serial ports on most computers use a subset of the RS -232C standard. The full RS -232C standard specifies a 25-pin "D" connector of which 22 pins are used. RJ-45 The RJ-45 style connectors and ports are also commonly found on Ethernet, serial and ATM IMA cards and interfaces. ... These are commonly referred to as Ethernet.