Kronos is an operating system with time-sharing capabilities, written by Control Data Corporation in the 1970s. Kronos ran on the 60-bit CDC 6000 series mainframe computers and their successors. CDC replaced Kronos with the NOS operating system in the late 1970s, which were succeeded by the NOS/VE operating system in the mid-1980s.The MACE operating system and APEX were forerunners to KRONOS.