Sunday, September 30, 2018

Practical thoughts on MS-DOS source code

I recently wrote that Microsoft released the source code to MS-DOS v1.25 and v2.0 on Github. This is a huge step for Microsoft, and I congratulate them for releasing these older versions of MS-DOS under the open source MIT license!

This source code release was significant because it resolved an issue from Microsoft's previous attempt to open the source code to older MS-DOS. In 2014, Microsoft released the source code to MS-DOS 1.1 and 2.0 via the Computer History Museum. Unfortunately, the license used in the Museum release was a "look but do not touch" license.

My understanding from lawyers who have explained it to me (I am not a lawyer) is that you can be "tainted" by knowledge of proprietary source code, under US law and under similar laws agreed to by partner countries. So anyone who read or studied the source code to MS-DOS 1.1 or 2.0 as it was previously released via the Computer History Museum license was not allowed to contribute to FreeDOS afterwards. We posted several notices to this effect on the FreeDOS website and elsewhere.

But this source code release of MS-DOS 1.25 and 2.0 uses the MIT License, which is not only a recognized open source software license, but compatible with the GNU GPL. This means the "taint" concern is effectively lifted.

While this is great, there's a practical side to the source code release. Note that these are very old versions of MS-DOS. FreeDOS has already surpassed these versions of MS-DOS in functionality and features. For example, MS-DOS 2.0 was the first version to support directories and redirection. But these versions of MS-DOS did not yet include more advanced features including networking, CDROM support, and '386 support such as EMM386.

It's great to see Microsoft open-source these old versions of MS-DOS, but what will be the practical impact on FreeDOS? I think Tom E. answered this well:
“Frankly, not so much. the relevant facts about MSDOS like internal structures, memory layout aso. have been re-engineered/disassembled, documented and commented by Andrew Schulman, Mike Podanowsky, and MANY others, and merged in an almost complete (and almost correct) documented DOS API by Ralph Brown. thanks to them, and there is close to nothing to be learned by studying old MSDOS sources.”

Eric A. adds a similar comment:
“Well, this is mostly interesting for historical research, MS DOS 1.25 had almost no features and 2.0 also is very far away from running most "normal" DOS software.”

So FreeDOS would not be able to reuse this code for any modern features anyway. But for basic features, such as weird edge cases or specific application compatibility, maybe developers can reference this code to improve FreeDOS.

Set your expectations appropriately. Thanks to Microsoft for releasing this source code under an open source software license (MIT) but don't expect this to have much impact on FreeDOS. We've already advanced well beyond MS-DOS 1.25 and 2.0.

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