http://www.computerhistory.org/press/ms-source-code.html
Sadly not in a more recognised open source license but a more "you can read it and fiddle with it on your own machines for non commercial purposes" affair, full license http://www.computerhistory.org/ms-dos-early-source-code/agreement/ . To that end and for practical purposes you are considerably better off looking up something like Freedos, dosbox or possibly even something in the reactos line of thought.
However if you ever wanted to see the things that MS started with then here is your chance.
Previously Apple, IBM and even some of the source code for the very first version of Adobe Photoshop have been released.
http://www.computerhistory.org/atchm/category/from-the-collection/
Source
http://www.theregister.co.uk/2014/03/25/microsoft_releases_operating_system_source_code/
Sadly not in a more recognised open source license but a more "you can read it and fiddle with it on your own machines for non commercial purposes" affair, full license http://www.computerhistory.org/ms-dos-early-source-code/agreement/ . To that end and for practical purposes you are considerably better off looking up something like Freedos, dosbox or possibly even something in the reactos line of thought.
However if you ever wanted to see the things that MS started with then here is your chance.
Previously Apple, IBM and even some of the source code for the very first version of Adobe Photoshop have been released.
http://www.computerhistory.org/atchm/category/from-the-collection/
Source
http://www.theregister.co.uk/2014/03/25/microsoft_releases_operating_system_source_code/