Time Sharing Operating System
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Time Sharing Operating System, or TSOS, was an operating system for RCA mainframe computers of the Spectra 70 series.
RCA was in the computer business until 1971. Then it sold its computer business to Sperry Corporation; Sperry offered TSOS renaming it to VS/9. In the mid seventies, an enhanced version of TSOS called BS2000 was offered by the German company Siemens.
While Sperry (Unisys after the company was renamed) discontinued VS/9 in the early 80's, BS2000, now called BS2000/OSD is still offered by Fujitsu Siemens Computers and used on their mainframe customers primarily in Europe.
TSOS was the first operating system that supported virtual addressing of the main storage. As the name suggests, it provided time sharing features. Beyond that it provided a unique user interface for both time sharing and batch which was a big advantage over IBM's OS/360 or their successors MVS, OS/390 and z/OS.