The TFileReadWrite structure.

 // FileRead, FileWrite
 TFileReadWrite       struct
  Result              word      // The function call result.
  FileHandle          byte      // The file handle to access.
  Buffer              byte[]    // The buffer to store read bytes or containing bytes to write.
  Length              dword     // The number of bytes to read or the returned number of bytes written.
 TFileReadWrite       ends

Possible Result values include Loader module error codes.