Xerox Operating System
The Xerox Operating System was an operating system for the XDS Sigma series of computers "optimized for direct replacement of IBM DOS/360 installations" and to provide real-time and timesharing support.
The system was developed, beginning in 1969, for Xerox by the French firm :fr:Compagnie internationale pour l'informatique|CII.
XOS was more successful in Europe than in the US, but was unable to compete with IBM. By 1972 there were 35 XOS installations in Europe, compared to 2 in the US.
