3.1-tan (Japanese: 3.1たん, 3.1-tan), also known as Ōbaba (Japanese: 大婆), is an OS-tan that depicts Windows 3.0 to 3.11. She is one of the lesser known OS-tans.
3.1-tan is a girl in a gothic lolita dress, depicted as the younger sister of 1.0-tan and the older sister of NT-Mama, as well as 95-tan's mother. Her manner of speech is similar to an old lady, often ending her words with "ja"「～じゃ」. She has an inseparable relationship with her black cat, DOS Kitty, due to how Windows 3.0x was heavily reliant on DOS. Now retired, she currently tends the family shrine.
Previously, it was assumed that 3.1-tan would have been a civilian on the sidelines of the OS Wars, but recent images of 3.1-tan in military uniforms and holding a sword imply a different character interpretation, that she may have played a proactive role in the wars.
- Windows 3.x, page about the OS itself and its family, that also lists alternate personifications.