Programs (also known as executables) contain binary code in a form that is ready to be run on a computer. Programs are written using a computer language (‘C’ or ‘C++’, for example), where the programmer writes the language-specific instructions using a text editor: this is known as source code. The source code is then compiled into instructions that can be interpreted by the computer.

The most common file extension for programs in a Microsoft® Windows® environment is EXE, but there are other files that contain program code, including COM and DLL. Batch files (which have the extension BAT) are themselves text files, but they contain a list of instructions for the computer to carry out unattended.