Nomyso is a Perl program which converts assembly language source files for MASM and TASM to NASM-compatible source files. The current version of Nomyso is 4.3. Changes from version 4.0 are better translation support for operations which use XMMWORD, QWORD, DQ, DD, and ST0-ST3.

You must have a copy of Perl to run Nomyso. Perl can be downloaded for most common operating systems at

Download the current version of Nomyso


Nomyso runs as any typical Perl program at the command line. Two parameters are required: the input file as MASM/TASM-format source, and the output file as NASM-format source. Nomyso supports a few options, which can be viewed by running Nomyso without any parameters.

Since Nomsyo was originally written simply to translate two specific source files for the FreeDOS project, manual edits will be necessary for most nontrivial MASM/TASM source files to ensure full NASM compatibility. A number of MASM/TASM commands are not supported and support for macro translations is limited. However, Nomyso has been increasingly successful in converting larger and more complicated programs with little or no manual intervention. Translation results will vary depending on the nature and complexity of the original source files.

Nomyso supports direct post- and pre-processing of translated lines via the -x and -xr options. This allows automating translation of source line exceptions and special cases, or extension of the normal translation process provided by Nomyso. For example, to fully automate the NASM conversion of the FreeDOS HELP source file CONIO.ASM, the option -x'/(^%define\s+.*\s)dword\s+/$1/i' can be used.

Future versions of Nomyso will continue to improve automatic translation compatibility with a wider range of MASM and TASM source files.


All support from the Nomyso developer is provided at the I Fix Scripts blog.

History Download the current version of Nomyso