Microsoft donated the source code of MS DOS 1.1 and 2 to the Computer History Museum (CHM), along with the first version of Word for Windows last month – Nirvana for retro-computing fans.
Version 1.1 of DOS, although very limited by todays standards fits into only 12KB of memory, which is tiny compared to today’s software. The Word document I typed this story onto was 58KB!! Keeping historic code like this allows us to see how software has evolved from being a primitive gimmick to becoming an integral part of our daily lives.
Microsoft has not made the code open source but has made it available under a research licence and available for download but it cannot be distributed further under the terms of the licence. You can download the source code and read more about DOS 1.1 here
DOS came into existence when Microsoft won a deal with IBM to provide them with an operating system, it gave them Q-DOS (Quick and Dirty Operating System) and renamed it as MS DOS in 1981. By 1989 Microsoft had gone through several iterations of DOS but by this point had produced Word as part of its Windows package – this proved a big hit and the rest as they say, is history.