To get the answer, just put a decimal point in the number "50"—my first Microsoft product was MS-DOS 5.0.

[Yeo Kheng Meng] didn’t cheat by simply running MS-DOS on a modern PC, either: he tested the client on a real 1984 vintage IBM 5155 Portable PC. This semi-portable PC/XT model sports a 4.77 MHz ...

Twitter user VirtuallyFun shared their cutting-edge 16 MHz Intel i386 MS-DOS 4 install on the 1987 IBM Personal System/2, which mainly lives on today in its legacy PS/2 peripheral connectors.

Mills, D. Q., and G. B. Friesen. Broken Promises: An Unconventional View of What Went Wrong at IBM. Boston, MA: Harvard Business School Press, 1996.