Tape Operating System <operating system> (TOS) An {IBM} {operating system} for {System 360}, used in the early days around 1965 to support the {IBM 360} model 30 et al. TOS was a predecessor to IBM's {Disk Operating System}. TOS died out really early as disks such as the 2311 and 2314 became common with the {IBM 360} whereas thet had been a real luxury on the {IBM 7090}. [Relationship to {BOS}?] (1999-01-20)