作業系統(2)

第二章 System Structures

An operating System provides the environment within which programs are executed.

User interface. Almost all operating systems have a user interface(UI). The interface cam take several forms. One is DTrace Command-line interface(CLI), which uses text commands and a method for entering them.

Another is a batch interface, in which commands and directives to control those commands are entered into files, and those files are executed.

Most commonly, a graphical user interface(GUI) is used. Here, the interface is a window system with a pointing device and direct I/O, choose from menus, and make selections and a keyboard to enter text.

On systems with multiple command interpreters to choose from, the interpreters are known as shells.

System calls provide an interface to the services made available by an operating system.

System programs, also known as system utilities, provide a convinient environment for program development and execution.

The kernel has a set of core components and links in additional services either during boot time or during run time. Such a strategy uses dynamically loadable modules and is common in modern implementations of UNIX.

Seven types of loadable kernel modules
1. Scheduling classes
2. File systems
3. Loadable system calls
4. Executable formats
5. STREAMS modules
6. Miscellaneous
7. Device and bus drivers.