X Window System core protocol: Difference between revisions

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The '''X Window System core protocol'''<ref name="sche-gett">Robert W. Scheifler and James Gettys: ''X Window System: Core and extension protocols, X version 11, releases 6 and 6.1'', Digital Press 1996, ISBN 1-55558-148-X</ref><ref name="rfc 1013">RFC 1013</ref><ref name="intr">Grant Edwards. [http://www.visi.com/~grante/Xtut/ An Introduction to X11 User Interfaces]</ref> is the base protocol of the [[X Window System]], which is a [[Computer network|networked]] [[windowing system]] for [[bitmap]] displays used to build [[graphical user interface]]s on [[Unix]], [[Unix-like]], and other [[operating system]]s. The X Window System is based on a [[client–server model]]: a single [[Server (computing)|server]] controls the [[input/output]] hardware, such as the [[Computer screen|screen]], the [[Computer keyboard|keyboard]], and the [[Computer mouse|mouse]]; all application [[Computer program|program]]s act as [[client (computing)|client]]s, interacting with the [[user (computing)|user]] and with the other clients via the server. This interaction is regulated by the X Window System core protocol. Other [[protocol (computing)|protocol]]s related to the X Window System exist, both built at the top of the X Window System core protocol or as separate protocols.

In the X Window System core protocol, only four kinds of packets are sent, [[Asynchronywikt:asynchronously|asynchronously]], over the network: requests, replies, events, and errors. ''Requests'' are sent by a client to the server to ask it to perform some operation (for example, create a new window) and to send back data it holds. ''Replies'' are sent by the server to provide such data. ''Events'' are sent by the server to notify clients of user activity or other occurrences they are interested in. ''Errors'' are packet sent by the server to notify a client of errors occurred during processing of its requests. Requests may generate replies, events, and errors; other than this, the protocol does not mandate over a specific order in which packets are sent over the network. Some extensions to the core protocol exist, each one having its own requests, replies, events, and errors.

X originated at [[Massachusetts Institute of Technology|MIT]] in 1984 (its {{As of|2006|alt=current}} release X11 appeared in September 1987). Its designers [[Bob Scheifler]] and [[Jim Gettys]] set as an early principle that its core protocol was to "create mechanism, not policy". As a result, the core protocol does not specify the interaction between clients and between a client and the user. These interactions are the subject of separate specifications,<ref name="gett">Jim Gettys. [http://freedesktop.org/~jg/roadmap.html Open Source Desktop Technology Road Map]</ref> such as the [[ICCCM]] and the [[freedesktop.org]] specifications, and are typically enforced automatically by using a given [[widget set]].