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The content of this article mainly revolves around what the UNIX operating system refers to. The content of the article is clear and clear. It is very suitable for beginners to learn and is worth reading. Interested friends can follow the editor to read together. I hope you can get something through this article!

Before you learn Linux, you have to mention UNIX. UNIX is the earliest developed operating system, while Linux is developed on the basis of UNIX. Linux and UNIX are widely used in various servers and are one of the most influential computer operating systems at present.

Before introducing UNIX, it is necessary for readers to understand what an operating system is.

What is the operating system?

The operating system is a computer program that manages computer hardware and software resources. it can reasonably organize the flow of computer work and is the interface between the user and the computer. at the same time, it also provides an operation interface that allows users to interact with the system.

The operating system manages all the hardware facilities of the computer. It can not only effectively control the correct operation mode of the CPU, but also distinguish and read the data in the hard disk. The process of realizing these functions mainly depends on the ability of the operating system to identify all the adapter cards, so that all the hardware of the computer can operate normally, so if there is no operating system, then the computer will not be able to perform its proper functions.

The operating system has the following four characteristics:

Concurrence

Concurrency means that two or more events occur at the same time interval. Microscopically, it usually means that the program is executed alternately over time periods. Share

Sharing means that the resources in the system can be used by multiple concurrent processes in memory. Sharing is divided into the following two ways:

Mutually exclusive sharing methods, such as printers and tape drives. Only one process is allowed to access the resource at a time.

Simultaneous access methods, such as disk devices. Virtual

Virtual refers to the transformation of a physical entity into several logical counterparts. For example: virtual processor, virtual memory, virtual external device. Virtual realization in the operating system is mainly through the use of time-sharing. Async

In a multi-program environment, multiple programs are allowed to execute concurrently, but due to the limitations of resources and other factors, the execution of the process is not always executed, but intermittently, when each process in memory will start execution and pause, and how much time each program will take to complete, all of which are moving forward at an unpredictable speed, which is the asynchrony of the process.

Note: the most basic features of the operating system are concurrency and sharing, which are conditions for each other.

What is UNIX?

UNIX is the earliest operating system, and its development process is long and tortuous, but it is precisely because of the emergence of UNIX that it has triggered the ideological change of the operating system, so that it still has a far-reaching impact on the current computer technology. The birth of the UNIX operating system is a legend in the computer industry, and it is a must for software developers to understand.

UNIX operating system is a multi-user and multi-threaded operating system. The so-called multi-user means that multiple users can use the UNIX operating system at the same time and do not interfere with each other when they do their own tasks, while multithreading means that any user can run multiple programs on the UNIX operating system at the same time.

A brief evolution of UNIX, as shown in figure 1:

The development process of UNIX

Fig. 1 the development of UNIX

More specifically, the UNIX operating system consists of the kernel, Shell, and programs:

Kernel: the kernel is the core part of the operating system. On the one hand, it allocates time and memory for programs, and on the other hand, it responds to system calls by handling file storage and communication.

Shell:Shell belongs to the interface between the user and the kernel. For example, when the user needs to log in to the system, the login program automatically checks whether the user name and password are correct, and then starts the program called Shell; when the program is completed, the system will give the user another prompt that the program has been terminated

Programs: Shell is a command line interpreter, and these commands are also part of the program, including files and processes.

Generally speaking, UNIX is a computer operating system, which is a control program specially used to coordinate, manage and control computer hardware and software resources. The UNIX operating system has the following advantages:

Multi-user, multi-threaded operating system and supports the architecture mode of multiple processors.

It is written in a simple programming language, which makes the system easy to understand and modify, as well as interpreters and compilers of various programming languages.

The use of powerful programmable Shell language to make the user interface beautiful and generous, simple and clear.

Open source.

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