Software
Operating Systems
An operating system operates your system. The main (or most popular) three OS groups are: Microsoft Windows, Mac OS X, and GNU/Linux.
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Windows
Windows is the most popular OS group in the world, especially for gamers. The latest version is Windows 10. Windows 7, 8, and 10 are free to download and can be installed on a newly built PC. Keep in mind that there will be some features unavailable in the free version until the operating system is paid for, and activated.
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Mac OS
Usually found on Apple computers. macOS and OS X are UNIX-based, and are marketed by Apple as being stable. You can try running one of these OS options on a normal PC, though this is also against Apple's Terms of Service and is therefore not advised, even if you purchase the OS.
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Linux
An open-source, free OS. You can legally install and use most variants of GNU/Linux without paying a at all. Try Ubuntu, Mint, or Gentoo.