Time Sharing Operating System
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TSOS or Time Sharing Operating System was an operating system for RCA (Radio Corporation of America) mainframes of the RCA 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 was offered by the German company Siemens and was called BS2000 here.
While Sperry (respectively 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. 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 as it simplified the operation.