PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems. History and versions PhysTechSoft was formed in 1991 in Moscow, Russia by graduates and members of MIPT, informally known as PhysTech. At the end of 1993, PhysTechSoft released the first commercially available PTS-DOS as PTS-DOS v6.4. The version numbering followed MS-DOS version numbers, as Microsoft released MS-DOS 6.2 in November 1993. In 1995, some programmers left PhysTechSoft and founded Paragon Technology Systems. They took source code with them and released their own version named PTS/DOS 6.51CD as well as S/DOS 1.0 ("Source DOS"), a stripped down open-source version. According to official PhysTechSoft announcements, these programmers violated both copyright laws and Russian military laws, as PTS-DOS was developed in close relationship...