The file is two lines of format information as ASCII text, followed by two concatenated gzipped ustar files.
The first line is the format version number padded to 8 digits, and is 0.939000 for all old-format archives.
The second line is a decimal string (without leading zeroes) giving the length of the first gzipped tarfile.
Each of these lines is terminated with a single newline character.
The first tarfile contains the control information, as a series of ordinary files, described in Debian Packaging Manual, section 2.2. The file control must be present, as it contains the core control information.
In some very old archives, the files in the control tarfile may optionally be in a DEBIAN subdirectory. In that case, the DEBIAN subdirectory will be in the control tarfile too, and the control tarfile will have only files in that directory. Optionally the control tarfile may contain an entry for `.', that is, the current directory.