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We know that computers can be used for work, study, entertainment, etc. In addition to the necessary computer hardware, software is also needed. Usually, we call a computer with only hardware but no software "bare metal", which cannot do any meaningful work. At present, software can be divided into two categories according to its use: system software and application software. System software is a program designed for computer systems to efficiently use and manage computer software and hardware resources and support the operation of application software. Such as operating systems, programming languages and language processing programs, network system software, system service programs, etc. Among them, Windows operating system is what we often use. Application software is a variety of programs that are user-oriented and written to solve practical problems. It can be written by users themselves or purchased. For example, office XP, Photoshop, Red Alert and so on, which we often use.On personal computers, there are five most commonly used operating systems: DOS, Windows, Unix/Xenix, and OS/2. DOS System-In the 17 years since its inception in 1981, DOS has undergone 7 major version upgrades, from version 1.0 to version 7.0 now, continuously improving and perfecting. Windows System-Windows is the first generation of window visual interface published by Microsoft in November 1985, which makes PC enter the so-called GUI (Graphical User Interface) stage. Unix system. Unix systems were initially used on small and medium-sized computers. Unix is a multi-user system, which generally requires more than 8M of memory and a large capacity of hard disk. Linux system-Linux is the largest free software in the world at present. It is an operating system with functions comparable to UNIX and Windows and has complete network functions.张老太太忽觉没了声音，还以为孙子们都走了呢。重拍将在法国4台播出（或多或少类似于BBC3）。　　一个行为正直严格自律的老村长，精心设计着自己退休后的晚年生活。一生忠诚于信仰的他，却在本性面前轻易地低下了头；一个污点掉落在命运蓝图上，他竭力去擦掉污迹，却剥开了一个黑洞，深陷其中。新的神秘召唤,围绕着寻找Kenchington的吊坠而展开,故事会带我们进入一个谋杀事件的世界,还有间谍,和丢失的图书.It is of great help to practice photography.