The X Protocol and XWindows

The X Protocol and XWindows
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

A Review

The Simple Case:
- What do you see (and why) after you first boot a non-windowing OS?
A More Complicated Case:
- What happens if you then ssh/telnet into a remote machine?

Introduction

History:
- Developed at MIT during the mid 1980s as part of Project Athena
Objective:
- A windowing system and graphical user interface for networked computers

Layering

In The 5-Layer View of the Internet:
- The X protocol is an application layer protocol
The X Protocol Itself:
- Consists of a device independent layer (for communications) and a device dependent layer (for graphics)

Architecture

X Client:
- Sends requests (for graphical operations, information) to the server
- Receives keyboard and mouse events from the server
X Server:
- Accepts requests and acts on them

Architecture (cont.)

The Server Side:
- Runs on the local machine (and displays graphics requests on it)
The Client Side:
- Runs on the remote machine (e.g., xterm) or the local machine (e.g., xclock)
- Client must be told what server to use using the DISPLAY environment variable

Message Types

Messages (cont.)

Messages (cont.)

Window Managers

Purpose:
- Controls the appearance of windows
- Provides a way for users to interact with windows
Examples:
- AfterStep (based on NeXT)
- Enlightenment (used with Gnome)
- WindowMaker
- Metacity

Desktop Environments

Purpose:
- A window manager plus an interface to the operating system
- Often include utilities and applications
Examples:
- Common Desktop Environment (CDE)
- KDE