Files with the extension ASM are source code files in assembler programming language. An assembly language is a so-called low-level programming language that represents a human-readable form of machine language of a particular processor architecture (eg, x86, MIPS, PowerPC).
ASM files can contain the source code for entire programs or only parts, for example data segments or functions which are referenced in another ASM file, ie dH.
ASM files are merely text files that can be processed by a compiler called an assembler. They can be opened and edited in any text editor, however it is recommended to use editors with developer functions such as syntax highlighting for easier work.
Each processor architecture has its own machine language and thus also assembly language. In addition, the assembler compilers of a processor architecture sometimes have different syntax. Therefore, with an ASM file, you have to know the architecture and (depending on the architecture) the compiler, in order to be able to compile this file.