A blast from the past: Disassembling DOS (2020)

The text discusses the disassembly of MS-DOS, focusing on understanding its internal workings by examining key functions like INT 21h. It explains the importance of disassembly in uncovering how DOS functions, especially when source code is not available. The chapter delves into dissecting DOS files like IO.SYS and MSDOS.SYS using tools like DEBUG to reveal the code handling INT 21h calls. It also touches on the legal aspects of reverse engineering and the availability of Microsoft's DOS OEM Adaptation Kit for deeper insights into DOS internals. The narrative distinguishes DOS from its components like COMMAND.COM and highlights the role of INT 21h functions in DOS operations. The discussion emphasizes the microkernel nature of DOS, likening it to a base for various extensions from Microsoft and third-party vendors. Overall, the text provides a detailed exploration of disassembling DOS to gain a comprehensive understanding of its functioning beyond surface-level interactions.