Which format is commonly used for executable and object code files on Unix systems?

The best answer for the format commonly used for executable and object code files on Unix systems is the Executable and Linkable Format (ELF). ELF is a widely adopted standard that provides a flexible way to structure executable files, object code, shared libraries, and core dumps. It is designed to support various architectures and operating systems, making it the default format for executables on many Unix-like systems, including Linux.

The ELF format allows for efficient memory management and modularity, facilitating the linking and loading of binaries. It contains headers that describe the file layout and segments that outline how to load the program into memory, which is crucial for execution.

Other formats like the Common Object File Format (COFF) are often associated with older systems or specific implementations and don't generally represent the standard for modern Unix implementations. The Portable Executable (PE) format is specific to Windows environments and is not applicable to Unix systems. The Graphic Interchange Format (GIF) is unrelated to executable code and is used for image files, emphasizing its irrelevance to this question.

Thus, the emphasis on ELF's design and compatibility highlights its significance and validity as the correct answer for executable and object code formats on Unix systems.