I remember that before I started this assignment someone told me there was this book called
Undocumented DOS which described how to write file systems in MS-DOS. I rushed to
my local bookstore and started reading there for about 2 hours, completely captivated, before returning home.
A whole new world was opening up to me: a large set of undocumented internal APIs allowing you to extend
MS-DOS with all sorts of wonderful functionality.
It was the world of TSR (Terminate and Stay Resident), EMS (Expanded Memory Specification) and the MS-DOS network redirector (accessible via INT 2F).
|Together with the fantastic book The Design and Implementation of the 4.3 BSD UNIX Operating System, which I had read for the same course, this started my long-life passion for low-level software.|