X

X See X Windows.

X11 A protocol suite for X Windows applications.

X.21 Recommendations developed by CCITT that define a protocol for communication between user devices and a circuit-switched network.

X.25 Recommendations developed by CCITT that define a protocol for communication between packet-switched Public Data Networks and user devices in the packet-switched mode.

X.400 International standard for a store-and-forward message handling system in a multivendor environment.

X.500 A standard which defines electronic mail directory services.

XBM An X-formated balck and white bitmap image.

XPM An X-formatted colour bitmap image.

XID eXchange IDentifier

XNS (Xerox Network Systems) Peer-to-peer protocol involving layered data communications protocols developed by Xerox and incorporated into Ethernet local area networks.

X Windows A program that provides Unix machines with a graphical user interface.