2001: Windows XP - History of Desktop OSs
Windows XP is born as the first major Windows release with a significant UI overhaul since Windows 95. It is also Microsoft's first complete 32-bit operating system. At the time, Microsoft said that Windows XP will be the operating system for the next billion of computers, since an estimated 1 billion PCs had sipped in the three decades before its arrival. Microsoft released several tiers of the OS, including XP Home, XP Professional, XP 64-bit Edition, XP Media Center Edition, and XP Tablet PC Edition.
Compiled from 45 million lines of code, it was criticized as an immensely bloated OS, but is remembered as Microsoft's most successful OS that has been available longer than any other Microsoft OS version to date. Due to a problematic Windows Vista, XP remained commercially available until October 22, 2010, well after the launch of Windows Vista and Windows 7. Support for the OS will remain available until 2014.