operating system （operating system, abbreviation OS） It is a computer program that manages computer hardware and software resources . operating system Need to deal with, such as managing and configuring memory 、 Determine the priority of supply and demand of system resources 、 Control input device and output device 、 Basic affairs such as operation network and management file system . operating system It also provides an interface for the user to interact with the operating system .

The operating system is flooded in our life and work , The more common ones are Windows,Unix,Linux,Ios, Hong Meng et al .

Catalog

operating system （operating system, abbreviation OS） It is a computer program that manages computer hardware and software resources . The operating system needs to deal with memory management and configuration 、 Determine the priority of supply and demand of system resources 、 Control input device and output device 、 Basic affairs such as operation network and management file system . The operating system also provides an interface for users to interact with the system .

One 、 Positioning of the operating system

Two 、 What is a process / Mission

3、 ... and 、 Process control block abstraction

Four 、CPU Distribute —— Process scheduling （Process Scheduling）

5、 ... and 、 Memory allocation —— memory management

6、 ... and 、 Interprocess communication

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One 、 Positioning of the operating system

Two basic functions of the operating system ：

1、 Prevent hardware abuse by out of control applications

2、 Provide simple and consistent mechanisms for applications to control complex and often disparate hardware devices

Two 、 What is a process / Mission

process （Process） A program in a computer is about a running activity on a data set , Is the system resource allocation and scheduling of the basic unit , yes operating system The foundation of the structure . In early process oriented computer architecture , A process is the basic execution entity of a program ; In modern thread oriented computer architecture , A process is a container for threads . A program is an instruction 、 Description of data and its organization , A process is an entity of a program .

process It's an abstraction of a running program by the operating system , In other words , You can think of a process as a running process of a program

 

3、 ... and 、 Process control block abstraction

Any real affairs should be managed inside the computer , It needs to be abstracted into a set of related , Integrated data . stay JAVA in , We can go through class / object To describe this feature . 

// The following code is JAVA Pseudo code form of code , Focus on explaining , Can't run directly 
class PCB {
    // Unique identification of the process  pid
    // Process associated program information , For example, the area where the program is loaded into memory 
    // The resources allocated to this resource 
    // Schedule scheduling information 
}

such , every last PCB Object represents a real program , That's the process .

The operating system then uses this data structure , For example, a linear table , Search tree, etc PCB Objects are organized , Easy to manage   Add, delete, query and modify when

Four 、CPU Distribute —— Process scheduling （Process Scheduling）

To facilitate discussion and understanding , Most of our scenarios assume a single CPU Single core computer

Operating system pair CPU Allocation of resources , Using a time model —— Different threads are used in different time periods CPU resources .

 

 

 

 

 

 

 

parallel vs Concurrent Kernel mode vs User mode ：

5、 ... and 、 Memory allocation —— memory management

The allocation of memory resources by the operating system , Using a spatial model —— Different processes use different areas of memory , They don't interfere with each other

 

6、 ... and 、 Interprocess communication

As mentioned above , A process is the smallest unit of resource allocation by the operating system , This means that each process cannot feel each other's existence , This is the original intention of the operating system to abstract the concept of process , This brings about a process to process relationship “ Isolation, ”.

But modern applications , To fulfill a complex business requirement , It is often impossible to complete independently through a process , There is always a need for coordination between processes , therefore , Between processes ” Information switching “ The needs of . The demand of interprocess communication arises at the historic moment .

at present , The interprocess communication mechanisms provided by mainstream operating systems are as follows ：

1、 The Conduit

2、 Shared memory

3、 file

4、 The Internet

5、 Semaphore

6、 The signal

among , Network is a kind of relatively special IPC Mechanism , In addition to supporting communication between two processes with the host , It also supports communication between processes on different hosts within the same network .