The Microsoft company made a present to all programmers eager to dig into some interesting stuff: they opened the source codes of MS-DOS v 1.1, v 2.0 and Word for Windows 1.1a. The MS-DOS operating system is written in an assembler, so the analyzer cannot be applied to it. But Word is written in C. Word 1.1a’s source codes are almost 25 years old, but we still managed to analyze it. There’s no practical use of it, of course. Just for fun.