I. Introduction to Operating Systems
1 operating system definition
The operating system is a system of computer system software, is the interface between the user and the computer system.
2 operating system's main purpose:
- Hardware and software management
- It provides a user interface
- Workflow rational organization of computer systems
3 operating system functions
- Process Management
- Storage Management
- Device Management
- Document Management
- The user interface
4 operating system mode
- Supervisor mode (kernel mode)
- Mesh state (user state)
- Why state and a mesh tube division states:
When the processor is in supervisor mode, the system may perform all the machine instructions, access to all resources, and has the ability to change the processor state; when the processor is in user state. Program can only execute non-privileged instructions. Therefore, the state is divided into cpu pipe state and the state purpose is to enhance the security of the system w
5 operating system features
- Complicated by
- Concurrency: more events occur in the same time period
- Parallel: multiple events occur at the same time
- Object is a process (dynamic) rather than program (static)
- shared
- Multiple processes share the limited resources of the computer, the operating system to allocate system resources and reasonable use. Resources are used in a period of alternating multiple processes.
- Share the mutex
- Before the release of the allocation of resources, can not be used by another process
- Simultaneous access
- As reloadable code disk file
- Resource allocation is difficult to optimize
- virtual
- Mapped to a physical entity corresponding to a plurality of logical entities - division / space division
- asynchronous
- The uncertainty of the process of implementation and execution time of the order
Second, the service provided by the OS
1 system calls
- Type of call systems (understand)
- Process control process scheduling classes
- Document management process scheduling classes
- Communication process scheduling classes
- Information maintenance process scheduling classes
2 operating system design
| Classification of the operating system kernel |
advantage |
Shortcoming |
example |
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| Simple structure |
Messaging reach the kernel of the user through the system call instead. Internal delamination method may be used. Kernel function directly implemented by the calling module when the communication module. |
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| Microkernel |
Kernel as a separate process running in privileged mode, communicating by message passing.
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User space and kernel space communication performance impact |
Tru64 Unix, QNX |
The traditional operating system design patterns
- Overall structure
- The entire operating system is a collection of a bunch of processes, each process can call any other procedure.
- Advantages: compact structure, a simple interface and high system efficiency
- Disadvantages: less independent module, the structure is not clear, are not easy to read easily understood that modifications inconvenient, indeed affect the whole body
- The modular structure
- Main modular programming technique, the entire operating system in accordance with the function is divided into several modules, the interface between the well and the binding module.
- Advantages: High operating system correctness can be a good adaptability
- Disadvantages: dividing block size is determined and the interface is relatively difficult to determine, and there are complex dependencies module before the operating system structure is not clear.
- Hierarchy
- A modular structure improvement. Operating system functionality according to flowchart call order and rules, the many modules are arranged in several levels, with individual dependencies between various levels. Dependent on the underlying level, does not constitute a cycle.
- Advantages: the operating system more simple and clear structure, higher accuracy.