IBM OS/2 1.0
OS/2 1.0 is the first version of OS/2. It was announced by IBM and Microsoft on April 2nd, 1987. It was marketed as a successor to DOS, although it was not meant to replace the DOS completely, but upgrade its capabilities. OS/2 1.0 supported multitasking, multi-threading, dynamic linking and virtual memory. It used a 16-bit protected-mode kernel, which required at least 286 CPU and caused many difficulties when mixing protected-mode and real-mode DOS applications.