X
 
 X Protocol
 
      A graphics description language that tells the X Server within the
      terminal how to draw the required objects on the screen.
 
 X Terminal
 
      A dedicated terminal platform that is designed to run X-server
      software; used with machines that run 680x0 processors.
 
 X Window System
 
      An industry-standard for graphical operating environments developed
      by the Massachusetts Institute of Technology (MIT) and Digital
      Equipment. The system allows users to simultaneously run and access
      applications in one or more host computers and display results in
      multiple windows on one display screen.
 
 X Window terminals
 
      A diskless terminal with large local memory resources and some
      intelligence.
 
 X-on/X-off
 
      A protocol that adjusts the flow of information for asynchronous
      serial transmission.
 
 X.21
 
      The ITU-TSS standard defining the interface between packet-type
      data terminal equipment and a digital interface unit.
 
 X.21bis
 
      A modification of the X.21 standard; it is identical to RS 232C at
      the physical level.
 
 X.24
 
      An international interface specification established by ITU-TSS
      international standards committee.
 
 X.25
 
      A ITU-TSS recommendation that defines the standard communications
      protocol for access to packet-switching networks.
 
 X.28
 
      DTE/DCE interface for a start-stop mode data terminal equipment
      accessing a PAD in a public data network situated in the same
      country.
 
 X.29
 
      The ITU-TSS standard for exchange of control information between a
      PAD and a host.
 
 X.3
 
      The ITU-TSS standard defining the PAD.
 
 X.400
 
      The ITU-TSS standard for electronic mail exchange.
 
 X.500
 
      OSI Service Directory standard.
 
 X.75
 
      The ITU-TSS recommendations for the interconnection and
      interoperation of two packet switched public data networks which
      both support the X.
 
 X/OPEN
 
      Licensing consortium for APIs.
 
 XA
 
      Extended Architecture (IBM).
 
 XBC
 
      External Block Controlled.
 
 XDMCP (X Display Manager Control Protocol)
 
      A login feature that transparently establishes a connection between
      the server (X station) and host.
 
 XDS
 
      Xerox Data Systems multiuser operating system. XENIX is a subset of
      UNIX.
 
 XMI
 
      Extended Machine Interconnect (Digital Equipment).
 
 Xmit
 
      Transmit.
 
 Xmodem
 
      Popular public-domain protocol for transferring files through
      asynchronous connections between personal computers. XMODEM is also
      a program for performing transfers, but the XMODEM protocol and
      functions have been incorporated into many personal computer
      communications products and are supported on other systems as well.
 
 XMODEM-CRC
 
      An advanced XMODEM protocol that utilizes a cyclicredundancy check
      (CRC) to detect transmission errors. defines a general purpose
      programmatic interface to OSI objectmanagement.
 
 XNS
 
      Xerox networking system: a mid-level ISO protocol used for
      primarily Xerox LANs.
 
 XOP
 
      Extended Operation.
 
 XOS
 
      Xerox Operating System.
 
 XPG
 
      X/Open Portability Guide; a set of publications that containthe
      specifications for the development of applications intended to
      beportable across X/Open certified complaint systems.
 
 XSI
 
      X/Open System Interface; includes extensions and annotations to
      allow the widest possible compatibility and portability for
      compliant applications.
 
 XTI
 
      X/Open Transport Interface; provides programming interfacesto
      services provided by the OSI Level 4.