Though DEBUG.EXE can send to CPU for execution just any machine code, variety of all x86 machine commands is too vast and may bewilder a newbie. fourth, it is able to interact with the user.third, it provides access to hardware and to OS structures.

second, it combines assembling and debugging capabilities.first, it gives the most clear notion of machine codes usage.Besides simplicity, DEBUG.EXE has a number of advantages, which make it the best suitable choice for this book : Codes that can't pass through MASM, can be compiled by DEBUG.EXE.įor firsthand acquaintance with programming the most simple assembler tool should be preferred. Similar unacceptable fragments were found in BIOS codes and even in loader modules of Windows XP operating system. Just because of this reason the MASM assembler wouldn't compile program examples shown in parts 9.06, 9.08, 9.10 of this book. Applications don't suffer because of that, but for research and system tasks it may become a sufficient obstacle. This great convenience, however, has its back side : freedom of manipulation with address space and with segment registers becomes lost. More sophisticated assemblers automatically compile headers and jump target addresses. Just that attitude has been inherited by DEBUG.EXE. Since then those assemblers, which couldn't automatically compile file's headers, have been regarded obsolete. For claiming memory requirements program's file headers were introduced. Each terminal was used to launch a separate program, and computer's memory had to be distributed between these programs. Over half century ago, computers implemented time sharing for several terminals. Are commands of archaic DEBUG.EXE worth the time getting acquainted with? This question invokes recollections.

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