Sankaku Channel/3.1-tan

Windows 3.1-tan (3.1たん) is one of the OS-tan canon. Depicted as a frail grey-haired young girl in a long frilly violet gown, with a "3.1" brooch on her collar. She has a quiet personality and is usually accompanied by either a black cat (sometimes nicknamed "DOS Kitty") or a small black-haired catgirl in a nurse's outfit, both representing DOS.

Source: ostan-collections.net