The initial operating system offered for both the Univac 90/60 and the slightly more powerful Univac 90/70 was OS-7. This had originally been offered for the Univac 9700 and was ported to the 90/70 when the 90/70 replaced the 9700 in the companies line of mid-size computers.
In 1975, VS/9 (Virtual System 9) was announced for the Univac 90/70 and 90/60. Initially, many 90/60 systems were under-powered running VS/9 and required memory and disk upgrades. VS/9 was derived from RCA's VMOS (Virtual Memory Operating System) and could host batch processing, traditional time-sharing, and transaction-oriented processing concurrently.
VS/9 was somewhat more than a traditional operating system of the time, rather it was what we might call a "hypervisor" today, hosting several operating systems in concurrent use. Although most batch-processing was handled directly by VS/9, TSOS (Time-Sharing Operating System) ran as a job under VS/9 and provided interactive time-sharing to multiple users.