The source code of MS-DOS is both secret and copyright-protected, so, as a Windows and DOS programmer, you can't study the code and figure out how this operating system works. If you could study the code, you would be able to optimize your Windows and DOS programs.
Now there's Dissecting DOS, the first book to take programmers on a fantastic voyage through the code-level guts of MS-DOS. The book features the complete source code for the DOS work-alike operating system RxDOS, which emulates and parallels the commercial system. Dissecting DOS explains the architecture, command structure, and operation of DOS and uses the work-alike RxDOS to illustrate the source code controlling vital DOS actions, such as processing function calls, file redirection, disk compression, memory management and device drivers.
Dissecting DOS reveals the details of DOS: