PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems.

PhysTechSoft was formed in 1991 in Moscow, Russia by graduates and members of MIPT, informally known as PhysTech.

In 1995, some programmers left PhysTechSoft and founded Paragon Technology Systems.

According to official PhysTechSoft announcements, these programmers violated both copyright laws and Russian military laws,[3] as PTS-DOS was developed in close relationship with Russia's military and thus may be subject to military secrets law.

Moreover, this release contained bundled source code of older PTS-DOS v6.51.