disassembly

A disassembler is a computer program that translates machine language into assembly language—the inverse operation to that of an assembler. The output of disassembly is typically formatted for human-readability rather than for input to an assembler, making disassemblers primarily a reverse-engineering tool. Common uses include analyzing the output of high-level programming language compilers and their optimizations, recovering source code when the original is lost, performing malware analysis, modifying software (such as binary patching), and software cracking.
A disassembler differs from a decompiler, which targets a high-level language rather than an assembly language. A fundamental method of software analysis is disassembly. Unlike decompilers, which make attempts at recreating high-level human readable structures using binaries, disassemblers are aimed at generating a symbolic assembly, meaning it's attempting to reconstruct the assembly closest to its executions. Disassembled code is hence normally more accurate but also lower level and less abstract than decompiled code and thus it can be much more easily analyzed.
Assembly language source code generally permits the use of constants and programmer comments. These are usually removed from the assembled machine code by the assembler. If so, a disassembler operating on the machine code would produce disassembly lacking these constants and comments; the disassembled output becomes more difficult for a human to interpret than the original annotated source code. Some disassemblers provide a built-in code commenting feature where the generated output is enriched with comments regarding called API functions or parameters of called functions. Some disassemblers make use of the symbolic debugging information present in object files such as ELF. For example, IDA allows the human user to make up mnemonic symbols for values or regions of code in an interactive session: human insight applied to the disassembly process often parallels human creativity in the code writing process.

View More On Wikipedia.org