Xerox Operating System

The Xerox Operating System, known as XOS, was an operating system for the XDS Sigma series of computers, developed beginning in 1969 by the French firm CII, which later became part of Bull. XOS was built to be optimized for direct replacement of IBM's DOS/360 installations, while also providing real-time and time-sharing support beyond what a straight batch system offered. It found more commercial traction in Europe than in the United States: by 1972 there were 35 European installations against only two in the US, and it ultimately struggled to compete against IBM's dominant mainframe operating systems. XOS was later merged with the Universal Time-Sharing System's capabilities into the successor CP-V operating system, and as a distinct, purpose-built system for the Sigma computer line it is separate from the general concept of an operating system.