There are some projects that aim to provide an environment where you can run old dos programs on newer Windows versions like Windows 7 or 8. (Such as dosbox and FreeDOS...)
Those projects are good, but they are not 100% compatible with all DOS programs. Until now Microsoft has not released any source code from DOS 6.22 so it was hard for those projects to reverse engineer it, so they aren't fully compatible.
I think today there is no more source code from DOS 6.22 inside Win7 or 8 (since it`s based on NT and not DOS) and if there still is it is only in the command line.
Microsoft wouldn`t have any loss of sales if they would make DOS 6.22 legal freeware and release the source code under an Open Source license. No new software is being developed or sold for DOS.
Releasing the source code also wouldn`t hurt and it could help those third party projects to become perfect.
People could also use it to learn assembly, use as a template for their OS, like Linux.
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