On Wed, 12 Oct 2011, Adam Sampson wrote:
designed the API to be similar to CP/M's to make
porting easy, but he
built the guts of the OS from scratch.
His blog's worth reading, particularly the early articles:
http://dosmandrivel.blogspot.com/
In 1982?, Dr. Dobb's published an article that he wrote ("An Inside Look
At MS-DOS"?) that talked about some of those issues.
Also, about the same time Cortesi? wrote "CP/M-86 V MS-DOS"? that was a
decent comparison of the internals.