[Operating system Notes] 1. Introduction

[Operating system Notes] 1. Introduction
Operating system Introduction convenience of the Operating System Effectiveness extensibility functions of the operating system OS as an interface between the user and the computer hardware system, that is, the OS is between the user and the computer hardware, when using the OS, note that, OS is a system software. You can use the following three methods to use computer commands: System calling methods: graphics, window mode, OS as the administrator of computer resources. Computer resources include: processor, memory, i/O devices and information (data and programs) OS functions: processor management: distribution and control processor memory management: Responsible for memory allocation and recovery I/O device management: responsible for the allocation and file management of I/O devices: Responsible for file access, sharing, and protection of OS, implementing the abstraction of computer resources. OS is a multi-layer system software deployed on computer hardware, they not only enhance the functions of the system, but also hide the details of hardware operations, which implement multi-layered abstraction of computer hardware. During the development of the operating system, the user (that is, the programmer) directly uses the computer hardware system by means of manual operation. The Simple Batch Processing System (Simple Batch Processing System) inputs a Batch of jobs offline to the tape and supervises the program on the System, under its control, this batch of jobs can be processed continuously one by one. Features: automatic, ordered, and single-track. Multiprogramming Batch Processing System jobs are first placed on the external storage to form a queue, which is called a backup queue. Then, the Job scheduler selects several jobs from the backup queue to transfer them to the memory, share the benefits of CPU and various resources in the system: Provide CPU utilization, provide memory and I/O device utilization, and increase system throughput. Features: multi-channel, no-order, and scheduling. The Time-Sharing System connects multiple terminals with monitors and keyboards on a single computer, and uses computers in interactive mode to share resources in the host. Features: multiplexing, independence, timeliness, and interactivity. Real-Time System can respond to external event requests in a timely or timely manner, process the event within the specified time and control the coordinated and consistent operation of all real-time tasks. Features: multi-channel, independent, timely, interactive, and reliable. The Development of Micro-computer operating system is configured on micro-computer operating system is micro-computer operating system single user single task Operating System (CP/M, MS-DOS) ---> single user multi-task (Windows) ---> multi-user multitasking (unix OS --> Solaris OS, Linux OS) Basic Features of the operating system concurrency (emphasis) concurrency and parallel: Two or more events occur concurrently at the same time: two or more events occur at the same time interval (there are multiple programs running at the same time) Process is the basic unit in the system that can run independently and be allocated resources. It consists of a group of machine commands, data, and stacks, and is an active entity that can run independently. A Thread can contain several threads. They can use the resources owned by the process and use the process as the basic unit for resource allocation, use a thread as the basic unit for independent running and independent scheduling. Shared mutual exclusion: Only one process (thread) is allowed to access the resource within a period of time. Simultaneous access mode: Allows multiple processes to access them simultaneously within a period of time, while macroscopic and microscopic interfaces are "alternate ". Concurrency and sharing are two basic features of the operating system, and they are mutually existent conditions. The so-called "Virtual" in a Virtual operating system refers to the use of certain technologies to convert a physical entity into several logical counterparts. Asynchronous Asynchronization means that the process is pushed forward at an unpredictable speed. Main features of the operating system processor management function Process Control: Creates processes for jobs, revokes terminated processes, and changes the status of control processes in operation. Process Synchronization: coordinates the operation of multiple processes (including threads). It is used for Process Communication in the process mutex mode and process synchronization mode to implement information exchange and scheduling between processes that cooperate with each other: every job waiting in the trunk column is usually executed only after scheduling. In a traditional operating system, the Job Scheduling and process scheduling are included. Memory Management Function Static Memory Allocation: the memory space of each job is determined when the job is loaded. You cannot apply for a new memory space or dynamically allocate it in the memory: the memory space of each job is also determined when the job is loaded. However, when the job is run, a new memory space is applied and the job is also running in the memory. In order to realize memory allocation, the memory allocation mechanism should have such a structure and function: memory allocation data structure, which is used to record the usage of memory space, as the basis for memory allocation. Memory allocation function. The system allocates memory space for user programs based on a certain memory allocation algorithm, the system recycles memory that is no longer needed by the user through the user's release request. Memory protection ensures that each user program runs only in its own memory space and does not interfere with each other. Address ing Memory Management provides the geographic ing function to convert the logical addresses in the address space into the physical addresses corresponding to the memory space. Memory expansion tasks in memory management do not lose the capacity to expand the physical memory, but use the virtual storage technology to logically expand the memory capacity, this makes the user feel that the memory capacity is much larger than the actual memory capacity. The device management function is used to manage all peripheral devices in the computer system. The main task is to complete the I/O Requests initiated by the user process and allocate the necessary I/O devices to the user process; improves the utilization of CPU and I/O devices, increases the I/O speed, and facilitates the use of I/O devices. Buffer Management introduces buffering, effectively easing the contradiction between the speed mismatch between the CPU and the I/O device (the contradiction between the high speed of CPU operation and the low speed of I/O ), improves CPU utilization. Common buffers: A single buffer mechanism, a two-way data transmission mechanism, and a public buffer pool mechanism for multiple devices to use at the same time. Device allocation allocates the existing resources of the system according to the user process's I/O request, and allocates the required devices according to a certain device allocation policy. Device processing is also called a device driver. Its basic task is to implement the communication between the CPU and the device controller, that is, the CPU sends an I/O command to the device controller, it is required to complete the specified I/O operation, and vice versa, the CPU receives the interrupt request from the Controller, and gives rapid response and corresponding processing. File Management Function file storage space management allocates graduation external storage space for each file, provides external storage utilization, and helps improve the file system running speed. Directory management creates directory items for each file and effectively organizes many directory items to conveniently retrieve files by name. File read/write management and file read/write management protection: reads data from external storage or writes data to external storage according to user requests. File Protection: prevents unauthorized users from accessing files, prevents unauthorized replacement for file access, and prevents incorrect use of file user interfaces. command interface online user interface: Provided by online users, consists of a group of keyboard operation commands and interpreter. Offline User Interface: this interface is also called the batch processing user interface provided by the batch processing job user. This interface consists of a group of Job control JCL. program Interface this interface is set for the user program to access system resources during execution. It is the only way for the user program to obtain the Operating System Service. It consists of a group of system calls, every system call is a subroutine that can complete a specific function. Whenever an application requires the OS to provide a certain service (function), it calls a system call with the corresponding function. 3. graphic interface graphical user interface uses a graphical operation interface, and uses a variety of icons that are easy to recognize to present system functions and various applications and files intuitively. Operating System Structure Design traditional operating system structure non-structured Operating System (First Generation OS) Modular structure OS (Second Generation OS) based on Decomposition and Modular principles to control the complexity of large-scale software. To make the OS have a clear structure, the OS is no longer directly composed of many processes, but is divided into several modules with certain independence and size according to their functions, module Interface Method hierarchical structure OS (Third-Generation OS) Client/Server mode (Client/Server or C/S) Client/Server mode (in fact our computer ~): Generally, multiple Network Workstations (clients) are connected to a LAN. Each client is an independent computer that can process local services or send messages to servers, to request a service. Server: it is usually a large computer with a Network File System or database system resident on it. It should provide one or more services for all users on the Internet. It remains in the working state and passively waits for requests from clients. Once a customer provides a service request is checked, the customer's request is completed and the result is returned to the customer. Network System: A system used to connect all clients and servers for communication and network resource sharing between them. Client/server interaction client Send Message Server receive message server send message client receive message advantages of Client/Server mode data distribution processing and storage, the client can process and store data, you do not need to store all data on the host. Ease of centralized management flexibility and scalability ease of application software adaptation