Atari DOS-tan represents the Operating System for the line of Atari 8-bit home computers. She has yellow eyes and blonde hair, braided in the back in the shape of the Atari logo, the braids ending in three small pigtails. She is a magician and her uniform contains many elements of the system embedded in it. Her magic wand is actually an Atari Remote Controller (from the video game line, but still compatible with the home computers) with an elongated receiver.
Being a magician reflects on Atari's marketing smoke mirrors to make their technically-inferior 8-bit computers competitive and more appealing. Her appearance as a magician is actually more impressive than her skills, but she is a very kind-hearted, fun-loving and innocent girl who is also very resourceful and able to do magic tricks using anything lying around. If not for her old-fashioned mannerisms and very antiquated prop comedy, she acts her appearance rather than her actual age.
In her family, she has several cousins who represent the Atari game consoles. However, she did not see them very often nor do they get along with her very well because of the similarities and partial interoperability between the 8-bit Atari computers and their game consoles and it seemed that she was interfering too much in their market. She also has a younger stepsister: Atari TOS-tan. And despite their differences and Atari TOS-tan's counterproductive antics, Atari DOS-tan loves Atari TOS-tan like a real sister would.
She spends nearly all her time with Commodore PET-tan and Apple ][-tan, forming a very inseparable, soft-spoken, tea-drinking trio. Although they used to be adversaries, they're now the best of friends