Summary: NASM/YASM requires word [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). MASM/TASM requires word ptr [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). They each choke on the other’s syntax. WARNING: This is very strange area without any ISO standards or easy-to-find … Read more
MASM (Microsoft Assembler) is the popular assembler for Windows. MASM is for 16-bit and 32-bit applications(x86). ML64 is the one for 64 bit sources (AMD64/x86-64) NASM (Netwide Assembler) is the popular assembler for Linux but is available on Windows too. NASM supports 16-bit, 32 bit and 64 bit programs. FASM (Flat Assembler) is available for … Read more
Section 2.2 of the NASM documentation is titled Quick Start for MASM Users which lists the important differences between NASM and MASM. NASM version 2.15 added some MASM compatibility, including a %use masm macro package. See section 6.5 masm: MASM compatibility. Even without the macro package, ? and DUP work in data directives like db, … Read more