frhed | fork of https | Editor library

Short answer: .exe ≠ .com

Hint: notice the MZ signature as two first bytes in the output of step 5 :-P

Long answer:

Microsoft's executable .exe format has more than just code. First of all it starts with a special signature (initials of the format's creator) followed by quite a bit of information that describes the organization of the code.

In contrast a .com file is just a code, meaning the very first byte of it is what gets executed once the file is loaded into memory.

The first disassembly you get is a wrong one (yes, the first one is wrong, not the second!) as it tries to start the parsing with the first byte instead of jumping on to the actual code.

dumpbin is intelligent enough to properly parse the header of that .exe file and begins the disassembly of the actual code.

Solution

If you'd like to compare the disassembly output you either have to make sure that your NASM is aware of the type of file and properly parses its header or... simplify your life and convert the .exe into a .com in which case both disassembling operations should produce the same output (barring potential bugs, of course)

The last time I was converting an .exe file into a .com was many years ago with a utility called exe2bin. A quick search online shows that this was during the days of Windows XP and is no longer shipped with the OS. Though I see no reason for it to not work if you download it from some place.