No, OS/2 2.0 and later could run any number of DOS and Windows 3.1 applications at once. I'm not sure about the 1.x series. You're probably remembering Window

No, OS/2 2.0 and later could run any number of DOS and Windows 3.1 applications at once. I'm not sure about the 1.x series. You're probably remembering Windows 9x's feature of being able to automatically reboot into MS-DOS for running games.