Compatibility with Earlier Versions of MASM

In many cases, MASM 5.1 code will assemble without modification under MASM 6.0. However, MASM 6.0 provides a new OPTION directive that lets you selectively modify the assembly process. In particular, you can use the M510 argument with OPTION or the /Zm command-line option to set most features to be compatible with version 5.1 code.

See Appendix A, “Differences between MASM 6.0 and 5.1,” for information about obsolete features that will not assemble correctly under MASM 6.0. The appendix also discusses how to update code to use the new features.