Here are some useful links if you ever need to use the Microsoft Macro Assembler (MASM), which assembles and links one or more assembly-language source files.
(e.g. if building the zlib compression library)
ml64.exe is the assembler that accepts x64 assembly language.
The ML and ML64 command line reference guide can be found at
I also came across a useful discussion in a forum on MSDN, How do I get Visual Studio 2008 to use ML64.EXE instead of ML.EXE in an x64 Build?