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Character information
Common name CTSS-tan
Also known as Compatible Time-Sharing System
Human name(s) Tessa Corbato
First appearance Dec 2007
Height 168 cm (5'6")
Hair color dark red
Eye color dark red
Weapon(s) Yet-unknown, may involve fire
Faction MIT Society and loosely associated with the IBMs.
Lineage MIT- direct descendant of Whirlwind
Rival(s) N/A
Technical information
System personified Compatible Time-Sharing System
Developer(s) MIT
Debut 1961
Latest release unknown, discontinued by 1973

Technical details

The Compatible Timesharing System, released 1961, is a small timesharing system built for the IBM 7094 computer. One of the first timesharing operating systems, it was developed by the Massachusetts Institute of Technology Computation Center. It's worth noting that the “Compatible” in CTSS' name refers to an earlier IBM OS, Fortran Monitor Program, which CTSS virtualized in order to complete batch processes.

While it had a short lifespan of twelve years and was only installed in two sites (both on the MIT campus) CTSS proved to be prolific; it influenced most timesharing systems to come, most notably CP/CMS, TSS/360 and Multics – the latter a direct descendant, built on and hosted by CTSS machines until it was self-functioning. The source code of CTSS was made open and freely available in 2004. In August of 2010, an operational 7094 emulator capable of running a functioning CTSS system was released.

Character details


CTSS-tan is depicted as a mature woman with wavy dark red hair, dark red eyes and small oval glasses. A sinophile, she dresses in Chinese-inspired Victorian-style clothing and partakes in Chinese cultural activities. She dresses simply and elegantly, reflecting the sensible nature of the system. Her mother is Whirlwind, and has two sisters who both outlived her: SAGE and PDP 1. She stands out as the only OS-tan in a family of hardware and hybrid -tans.

CTSS is quiet and reserved, traits sometimes mistaken for emotional distance or coldness. In reality she is actually quite kind and caring especially toward her “kids” and students. She considered Multics her child and took care of her when she was too young, and sick, to care for herself; one of her greatest achievements in life was raising her into healthy adulthood (and furthermore securing an heir).

Alternate character interpretation

She is usually portrayed as a deceased character. Seeing that CTSS was Open Sourced and can now be used in emulators, another interpretation is that she was resurrected, but if so, her whereabouts haven't been discussed yet.

History and background

Along with Multics, CTSS also taught many young timesharing OS-tans of the day, including CP/CMS, TSS/360 and ITS. It is unknown how she feels about her most famous descendant, Unix, as the two never had an opportunity to meet; but has been speculated that she would have looked upon her simple granddaughter favourably.

While technically an IBM-tan, CTSS had no allegiance to the empire, scorning them for the academic intelligentsia of MIT. The only IBM-tans she regularly worked with, and had affection for, are FMP-tan – her assistant – and CP/CMS, one of her students.

CTSS never left Cambridge, Massachusetts and largely ignored the outside world. She had a few outsider friends however, most notably DTSS-tan. While CTSS' short life ended in 1973, her legacy lives on to this day and has no end in sight.

Since CTSS became Open Source in 2004, and at least one emulator already being developed, it's possible she could be completely resurrected.