How does the "Compatibility Mode" in Windows work?

Compatibility mode is achieved using so called shims. There is a good article on TechNet describing how these work. Windows application files contain an import table which tells the application loader which DLLs the application needs and which functions it uses from them. A process might for example reference in the . When a program shall run in compatibility mode, then the shim is put between the application and the shim replaces the function, so that the application does not call from but the…