GOB files are a repository for many other files, and are by far the best way to distribute add-on levels.
They contain a header with a signature, a data part and an index part.

GOB_Header IS { GOB_MAGIC char[4] // 'GOB' followed by 0x0A MASTERX long // offset to MASTERN }

The embedded files follow, then comes the index.

GOB_Index IS { MASTERN long // number of files in the GOB INDEXES GOB_Ix_Entry[n] // one index entry per file }

Where:

GOB_Ix_Entry IS { IX long // pointer to start of the file LEN long // length of the file NAME char[13] // name of the file, null terminated }