Microsoft's Windows XP has been officially supported for over 12 years but its development history actually goes back even further than that under the code name "Neptune."



From Neowin:

Microsoft will release the final software updates for Windows XP to the general public today (some businesses and governments have special support deals that will extend beyond April 8th). That means that for the regular XP user, there will be no more patches for the OS that launched over 12 years ago.

Yet the development of what would be called Windows XP extends much further than its launch date of October 25th, 2001, In fact, the OS is actually the end result of a merger of two projects and teams in the Windows division.

  A (very) brief history of Windows XP