The Theorysonic Operating System, often abbreviated as TS-OS or TS-OS 1 by fans, is a graphical operating system developed and released by Theorysonic and the first version of TSUG. Theorysonic Operating Systems was considered to be the world's very first operating system.

Released in 1973, the Theorysonic Operating System was the important milestone for Theorysonic, as it introduced the TS-OS line, which will later be replaced by the TS-UGOS/TSUG line.


The development of TS-OS began in 1965. TS-OS 1 took eight years to develop before being released.