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OS-02 Functions and Structures

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Overview

Operating systems provide an environment for program executions and services to programs/users

overview

Functions

User Interface

Shell: A computer program that exposes an OS’s services to a human user or other programs. OS shells use either a command-line interface (CLI) or a graphical user interface (GUI)
An interpreter

CLI

Shell：

  • Built-in commands: The interpreter contains the code to execute the command.
    • 直接执行 eg. cd
  • System program commands: The command is a program name.
    • 查找系统文件执行 eg. ls

System Calls

Mode

  • User
  • Kernel
    转换：系统调用，中断，异常

API

System calls are mostly accessed by programs via a high-level Application Program Interface (API) rather than direct system call use.
性质：

  • 易用：无需了解底层实现，直接调用
  • 可移植：API具有跨平台兼容性
  • 安全：直接调用与内核交互

Parameter Passing

  • 寄存器：快，少
  • 内存表
  • 栈

The last two methods do not limit the number or length of parameters being passed 性能损耗

Types

Type 1: Process control
  • Control the current process: end， abort， execute， load……
  • Control a different process
  • Allocate memory and release memory
  • Debugger
  • Locks for managing access to shared data between processes
Type 2: File management
Type 3: Device management
Type 4: Information maintenance
Type 5: Communications
  • message passing model 内核中转，离散
  • shared-memory model 共享物理内存
Type 6: Protection

System Services

In computer hierarchy, system services are higher than system calls.

System services use system calls to interact with the OS kernel

Programs

  • System Programs：Login program, shell, window manager
  • Application Programs：Email, web browsers, gaming software, word processors

Why Applications are Operating System Specific：

Reason: Each operating system provides its own unique system calls

eg. file format

Services

  • File management
  • Status information
    • Some systems implement a registry (注册表) - used to store and retrieve configuration information
  • File modification
  • Programming-language support
  • Program loading and execution
  • Communications
  • Background Services
    • Known as services, subsystems, daemons

Operating System Structures

  • Simple Structure – MS-DOS
  • Monolithic (单体)Structure – Original UNIX
  • Layered Approach
  • Microkernel System Structure - Mach
  • Hybrid Systems - windows, macOS, Android

Virtual Machines

visulization

Summary

topics