Introduction to Operating System

Concept

OS Elements

• Abstractions
  • process
  • thread
  • file
  • socket
  • memory
  • page
• Mechanisms
  • create
  • schedule
  • open
  • write
  • allocate(分配)
• Policies(策略)
  • least-recently used(LRU)
  • earliest deadline first (EDF)

关于 Mechanisms 和 Polices 的区别我其实迷惑了很久。

其实总结出来很简单 Mechanisms 机制 指的是 what to do

Polices 指的是 how to do

也可以这样理解机制是策略的更高一层抽象，策略是指具体如何实现的方式，机制则是我需要这个功能，但是不关注实现。

举个例子就是 Linux 内核的调度器（scheduler），提供了任务调度需要的原语操作和结构，并且实现了多种调度算法。

Process

what is a Process : state of a program when executing loaded in memory. (active entity)

• instance of an executing program
• Synonymous with "task" or "job"

A process is like an order of toys

• State of execution

  • program counter
  • stack

• parts & temporary holding area

  • data. register state, occupies state in memory

• may require special hardware

  • I/O devices

what does process look like ？

Process Control Block

• PCB created when process is created.
• certain fields are update when process state changes
• other fields changed too frequently

Context Switch(上下文切换)