COFF

COFF, or Common Object File Format, is a binary file format used for executables, object code, and shared libraries. It originated in the 1980s as a standardized object-file format for several Unix-like systems and hardware families, succeeding the older a.out format. Although many Unix systems later migrated to ELF, COFF variants persist in Windows as MS COFF, and in the Windows Portable Executable (PE/COFF) format that underpins modern Windows executables and DLLs.

A COFF file is organized into a header, an optional header for executables, a table of sections, and the sections themselves, which contain code, data, and other resources. It may also include a symbol table and relocation information, used by linkers and debuggers. The exact contents and layout vary by variant, with some adaptations tailored to specific operating systems and toolchains.

Variants and influence: MS COFF is the Windows variant used as the basis for the Windows-specific PE/COFF format, which adds Windows-directed headers and data directories while preserving much of the COFF structure. GNU COFF and related variants were used by various Unix-like systems and toolchains, particularly in the 1980s and 1990s, before ELF became dominant on most platforms. The COFF lineage thus helped shape several modern object and executable formats, including PE/COFF.

Current status: ELF is the predominant object and executable format on most Unix-like systems today, while Windows continues to rely on the PE/COFF lineage. COFF remains relevant for historical context, certain embedded toolchains, and compatibility with older software, with many modern toolchains providing support for COFF as part of broader multi-format capabilities.