Atari TOS is a variant of Digital Research's GEM OS ported to the Atari ST computers and was very commonly used by musicians as a music sequencer and to control musical instruments and was a main competitor to the Amiga and Apple //GS.
Atari TOS-tan is represented as a diva and singer formerly of idol status. She has long, wavy light blue hair and teal eyes; wears a green+white minidress with an Atari logo sash, a teal jacket, long green socks and dark green dress shoes. TOS-tan constantly obsesses over her looks, worried over what she believes is her fading beauty, follows trends seriously and is in extreme denial about getting old and not being the must have system anymore.
She is GEM-tan's twin sister but GEM-tan and TOS-tan were separated at a very young age (too young to remember each other), with TOS-tan living with her stepsister Atari DOS-tan. Following the traditions and business of her stepfamily, TOS-tan was supposed to be a magician but was much more of a song-and-dance performer. She had a lot of pizzazz, but neglected her magical skills and also helped her company run itself out of business with so many expenses.
She is somewhat of a loner but is best friends with Barbie Linux-tan, who is always glad to help her out with fashion tips.
When she was in her prime in the 1980's, TOS-tan was a bold and confident idol with legions of admirers that fought tooth and nail to protect her. She is now affiliated with the OS-tans of the Binteeji Renmei, including her true sister. However they are not very close though. While they may be able to get along with each other, their interests and personalities have diverged so much due to several years of separation, the circumstances and experiences each one has been through as well as the fact that TOS-tan distances herself from the Vintage-tans not just to avoid doing chores, but also because she does not want to be associated with them for being old.