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1.
Os-tans are anime personifications of operating systems as girls. Another name for it them is OS-girls. It all started when some random guy in Japan working at futaba channel thought Windows ME was like a tempermental troublesome girl who did all kinds of stupid things that lacked common sense.
person1: Xp-tan is a os-tan she has really big boobs!
Other person: YOU ARE PERVE!
by clueless_furball October 31, 2006
 
2.
A phenomenon started on futaba-channel where people made personifications of the operating systems out there. Find a long and better description at http://en.wikipedia.org/wiki/Os-tan
Geek1: XP-tan rocks so hard!
Geek2: All of the OS-tan's are so cute~ X3
Geek3: Yeah right.....
by Denny Lindberg June 20, 2005