MS-DOS executables with the COM extension can
be unassembled by the DEBUG command.
DEBUG <filename> enter
U enter
this will display the assembly language mnemonics
for the machine language of the program.
studying short simple programs with this method
is one of the best ways to learn what's
really going on inside the computer.
For more sophisticated, high level programming/debugging,
every programming language/system usually
comes with a debugger. They can single step through
a program, but as far as I know, decompiling is an art, not a science.
That is, no program will decompile in a fully automated fashion unless
all debugging symbols are embedded in the prog.
Such symbols aid developers in debugging, but are stripped
out when programs are released on the market.
