5 years ago today Windows XP was launched worldwide after it had RTM'd a month earlier.
It has been without a doubt the longest running operating system Microsoft has ever produced. Microsoft typically updated the client version of Windows every 2 years with Windows 95 being released in early 1996, the successive OSR updates until 1997 when Microsoft were hammered by anti-trust cases for bundling Internet Explorer 4.0 with Windows 95 OSR2, Windows '98 in 1998, Windows 98 Second Edition in 1999 and Windows Millennium in the February of 2000 after an extremely short beta cycle.
The flop that was Millennium was a last ditch attempt to salvage what was left of the outdated 16-bit legacy kernel, it was never at the top of Microsoft's comparison charts when Windows XP became available, they typically used Windows 98 SE as an example of how far the client version had come by switching to the proven NT kernel, offering for the first time the kind of stability only the industry had enjoyed with Windows 2000 Professional, the business workstation version of Windows.
Now, 5 years later Windows XP has been released with as many as 5 different flavors of which includes a 64-bit version and the latest version you can buy in the stores is Windows XP SP2b (an updated Service Pack 2 version). SP3 has been pushed back as far as 1H of 2008, long after its successor Windows Vista will be sitting on store shelves.
Less popular additions to the client version of Windows are WGA (Windows Genuine Advantage) and "Activation" a technology that "calls home" and verifies the product key. Both of the above, like all previous versions of Windows however have been circumvented at least once and Microsoft continues to make it harder to pirate Windows and its other software packages. Lets hope Microsoft also goes as far as to "improve" its pricing after reeping the benefits of less pirating and more sales.