The Computer History Museum has released the source code for MS-DOS 1.1, 2.0 and Word 1.1a



From OSNews:

The Computer History Museum announced today that it has, with permission from Microsoft Corporation, made available original source code for two historic programs: MS-DOS, the 1982 "Disk Operating System" for IBM-compatible personal computers, and Word for Windows, the 1990 Windows-based version of their word processor.

  Source code for MS-DOS 1.1, 2.0 and Word 1.1a released