NOS (Network Operating System) is a discontinued operating system with time-sharing capabilities, written by Control Data Corporation in 1975.

[2] NOS ran on the 60-bit CDC 6000 series of mainframe computers and their successors.

NOS replaced the earlier CDC Kronos operating system of the 1970s.

NOS was intended to be the sole operating system for all CDC machines, a fact CDC promoted heavily.

From NOS Version 1 Terminal User's Instant Manual, CDC, 1975–1980.