X.25
A popular standard for packet-switching networks. The X.25 standard was approved by the CCITT (now the ITU) in 1976. It defines layers 1, 2, and 3 in the OSI Reference Model.
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- XVCD
Short for eXtendedVCD it is a non-standardized recording format that offers features similar to VCD, however it can use a higher resolution to produce higher video quality. XVCD uses MPEG1 video. It can be played on some standalone VCD-compatible players, and on computers with a CD or DVD-ROMs with the use of compatible software.
- X.400
An ISO and ITU standard for addressing and transporting e-mail messages. It conforms to layer 7 of the OSI model and supports several types of transport mechanisms, including Ethernet, X.25, TCP/IP, and dial-up lines.
- X.500
An ISO and ITU standard that defines how global directories should be structured. X.500 directories are hierarchical with different levels for each category of information, such as country, state, and city. X.500 supports X.400 systems.
- X.509
(n.) A widely used standard for defining digital certificates. X.509 (Version 1) was first issued in 1988 as a part of the ITU X.500 Directory Services standard. When X.509 was revised in 1993, two more fields were added resulting in the Version 2 format. These two additional fields support directory access control. X.509 Version 3 […]
- X-Window
A windowing and graphics system developed at the Massachusetts Institute of Technology (MIT). MIT has placed the X-Window source code in the public domain, making it a particularly attractive system for UNIX vendors. Almost all UNIX graphical interfaces, including Motif and OpenLook, are based on X-Window.