Windows
Windows is the series of OS of Microsoft. Version 1.0 was put on sales in 1986. Windows 3.1, which was put on sales in 1992, was explosively spread as standard OS corresponded with PC/AT. Windows was an extension software to construct GUI environment in MS-DOS. Windows 95, which was sold in 1995 as a successor of Windows 3.1, started working as independent OS.
In 1998, windows 98, which is a successor of Windows 95, was put on sales (Windows Me, which is the upgraded version) and it has become the standard of OS for personal computers.
On the other hand, Windows NT series, which was put on sales in 1993, has a totally different kind of fundamental structure from Windows 3.x/9x. As a genuine 32 bit OS, it has greatly higher stability and prominent performance, and excellent security.
Windows NT and Windows 9x have the same API called Win32, so most of application softwares with Windows 9x can be used in Windows NT as well.
Windows NT series' OS has gained Windows 9x's functions from Windows 2000 for server workstation high end PC. Windows XP, which is a successor of Windows 2000, has installed NT-based system even for home personal computers and all x86 computers have been replaced with NT base. As a result, 9x carnal based products installed in Windows 95/98/Me do not exist any more.