1.0-tan (Japanese: 1.0たん, 1.0-tan), also known as Oichi (Japanese: お壱), is an OS-tan that depicts Windows 1.0x. She is one of the lesser known OS-tans.
She is depicted as the matriarch of the Windows-tans, and the sister and friend of 3.1-tan. Her hobbies are origami and Reversi. These hobbies are derived from the inability to stack windows on top of each other in Windows 1.0, so the windows were arranged like origami papers, and Reversi was commonly featured in screenshots of Windows 1.0.
She normally wears a kimono, but 3.1-tan has sometimes forced her to wear strange outfits. Her favorite food is tsubuan (red bean paste) yokan.
Being born in the Showa period, as per Windows 1.0's release date, she has a retro, old-fashioned mindset and is profoundly nostalgic. She is usually confused by the gap between past and present.
If and when she is angered, she can produce laser beams from her eyes.
- Windows 1.0x, page about the OS itself that also lists alternate personifications.