Operating System Overview
1.1 operating system objectives, roles and models
1. OS targets
Convenience: Users need to understand the underlying hardware, without having to use 0,1 machine language operations. (Can Say by hand, using tools into the Stone Age.)
Effectiveness: CPU, I / O, memory management and other specialized rationally organized to manage and improve the utilization of resources.
Scalability: expanded applications; adapt to hardware and system architecture development, expansion of the underlying management module.
Openness: network environment, follow the open Internet standards.
2. OS role
1) as an interface between the user and the computer system hardware (target reached convenience)
2) OS as a manager of computer system resources (effectiveness to achieve the target)
3) OS as the expansion machine
1.2 operating system development process
1) Manual operation
2) off an input / output (Off-Line I / O) mode
3) single-batch system (Simple Batch Processing System)
4) Multi-batch system
5) time-sharing system (time-sharing system)
6) real-time system (Real-Time System)
1, to promote the OS bud development, the main driving force of change:
1) user-friendly
2) increase computer resource utilization
3) the continuous upgrading of hardware devices: 8bit -> 16,32
4) the development of computer architectures: single-CPU, multi-CPU, network
2, OS classification
(1) single-user OS: supports only one user running the job.
(2) Batch OS: Users submit jobs to the batch to the computer.
(3) time-sharing OS: allows multiple users to interact with the computer system.
(4) Real-time OS: able to respond to randomly occurring external events, and make rapid processing of external events, the request signal from the outside and to respond within a defined time frame.
(5) Network OS: for multi-user on the network, the network provides the basic functions needed to operate, such as file sharing, memory management and task scheduling and other processes.
(6) distributed OS: is the most advanced operating system, manage the entire system (including network) all resources, responsible for the allocation and scheduling of all resources, division and specific arrangements, information transfer and control tasks.
(7) Embedded OS: the application closely integrated, highly dedicated, can be cut.
3, comparison of a distributed OS and network OS
1) of the distribution (distribution of both control and treated)
- Reside distributed OS is not concentrated on a single site, but uniformly distributed over the system compared to the respective site, so that the processing and control functions of the OS is distributed.
- The computer also has a distribution network processing function, the control function of the network, is focused on a host or network server, or that control is centralized. Processing is distributed.
2) Parallelism
- Distributed processing system having a plurality of processing units, the distributed OS task allocation program may be assigned a plurality of tasks to a plurality of processing units, so that these tasks are performed in parallel, thereby speeding execution of the task.
- Computer network, each user typically one or more tasks on their own (local) computer processing, therefore, no task allocation functions in the network OS.
3) transparency
- OS well distributed implementation details are hidden inside the system, such as: the physical position of the object, concurrency control, system fault, etc., it is transparent to the user. When a user accesses a file, simply provide the file name without having to know which it is resident on the site, you can access it, that is, the physical location is transparent.
- The OS network, there is a certain transparency, but it mainly refers to the operation to achieve transparency. Such as: When a user wants to access files on the server by issuing the appropriate file access command, without knowing the file access is how to achieve.
4) sharing
- Distributed systems, distributed across various sites of software and hardware resources, available to all users of the system-wide sharing, and can transparently access to them.
- OS can also provide network resource sharing, but are mostly shared resources provided in the host or a network server, and the resources on other machines, can only be used exclusively by the user of the machine.
5) robustness
- Distributed processing system and distributed control function, minimize the impact of any failure on the stand, do not give the system, and, when a device fails, the system reconfiguration may be accomplished by fault tolerance, the system can normal operation, therefore, the system is robust, i.e. have good availability and reliability.
- Network OS, which is mostly concentrated in the host control function or a server, the system has the potential unreliability, in addition, the function reconfigurable system is also weak.
The basic operating system characteristics 1.3
1, concurrent concurrence
Difference between two concepts
parallelism: two or more events occur at the same time
concurrency: two or more events occur at the same time
2. sharing sharing
system resources available to a process (thread) memory multiple concurrent execution of common use. There are two main ways to share:
exclusive sharing:
on the critical resources (such as printers) In this manner, the resources allocated to the front was not released after a process, other processes can not be used.
Critical resources (exclusive resources): a period of time only allows a process to access the resource.
At the same time access:
to allow "simultaneous" access to resources (such as disk) In this manner, but "at the same time" is still "macro micro parallel serial", not true at the same time
3. Virtual virtual
through some kind of technology to become a physical entity corresponding to the number of logical product (the user feels something), in two ways:
time-division multiplexing
a people sharing the article is used, a period of time on the performance of this article is available to everyone has one virtual 1 to n.
Space division multiplexing
4. asynchronism asynchrony
execution order refers to the process and the uncertainty of the execution time of the
speed of the process unpredictable
due to resource and other constraints, the process usually can not finish in one go perform multiple processes concurrently executing a "stop-go", and unpredictable run each process advancement speed; allow asynchronous, but the result should be correct, as long as the same environment, regardless of speed, the result should be the same (reproducibility), which requires mutual exclusion and synchronization means guaranteed.
1.4 The main function of the operating system
- Processor management functions (operations management)
- Memory management functions
- Device management features
- File management functions
- The user interface