The previous section about the history of Linux, the major Linux vendors are based on the GNU Project all open source software to build their own Linux distribution, a complete Linux distribution can be divided into the following four hierarchies:Base System = X Protocol + Windows Manager = Application
1. Base System
The so-called base system, which is a minimal base, needs to include some of the prerequisites for open source components such as kernel, filesystem, glibc, Bash, and so on. the ultimate level of this minimal system is the ability to launch our command-line character Control terminal, a bash environment, so that a minimal system can be streamlined and controlled within dozens of m of size.
2. X Protocol
When we have built the smallest basic system, such a system only supports the command line character terminal mode, but does not support the graphical interface, if you want to enable our Linux system to support the graphical interface, must have X protocol support, based on such an X protocol, The Windows manager of Linux can be built at the minimum system level. X Protocol is just a protocol, what is the specific implementation of such an agreement? In the early days of Linux, through the XFREE86 to achieve the X protocol, after years of development, XFREE86 has been replaced by today's X.Org project. whether it is XFree86, or the current x.org, in the implementation of the X protocol, is based on the C/S architecture, that is, x Server and X Client interaction mode. The relationship between x Server and x Client is described in more detail in the next section. Here you just need to be clear: if we need to support a graphical interface, it is necessary to have X-related components as a bridge of communication. of course, X is not the only bridge, there are new alternatives such as Wayland have been available, but not yet mature, perhaps someday in the future, Wayland will replace the present X.
3. Windows Manager
With the support of the X layer, the vast majority of open source software developers or development organizations, can be based on such an interface to develop the upper-level graphical window manager, Windows Manager, such as our well-known kde,gnome, XFCE, Openbox, etc., These graphical desktop environments are a concrete implementation of the X client mentioned above to communicate with X server interactively. in the chapter, we will explain the relationship between x Server, x Client, Xlib, QT, GTK, KDE, and Gnome.
4. Application
Application refers to our top-level graphical applications, such as Liberoffice Office suite, Firefox,thunderbird,pidgin, etc. Most of the graphical applications in the Linux system are based on QT or GTK + development kits, and of course there are applications written like Java, Python, and so on. In conclusion , the four-level GNU project component described above by the Linux Distributor will ultimately provide the user with a complete Linux operating system, with a structure diagram showing the Linux hierarchy described in this section:transferred from: http://blog.chinaunix.net/uid-26838492-id-3156661.html
Linux Architecture (II): Linux system hierarchy
