I have compared several tar implementations with the standard.

	(IEEE/Posix1003/IEC-9945-1 Standard Data Interchange format)

Although the standard now also defines cpio as an exchange format, I cannot
recommand the cpio archive format for data exchange. There are at least 6 
totally incompatible archive formats - all covered by the name "cpio".
It is most likely, that you are using an archive format that other cpio
implementations will not understand at all.

Tar in general will at least extract most of the files if you are using a
different implementation to extract the archive.

I've had a look at the following implementations:

	Index:	Program description:		Source of program:
	=====	====================		==================
	1)	bsd 4.3 tar			(Regents of UCB)
	2)	pax ustar i.e. SunOS 4.1	(USENIX)
	3)	tar on  Solaris 2.3/2.4/2.5	(Sun/AT&T ??)
	4)	gnutar	1.11.8			(gnu)
	5)	gnucpio 2.3			(gnu)


Summary:
	1)	bsd 4.3 tar
		Pre Posix 1003.1
	
		- Miscomputes the checksum. Therefore it is not able to extract 
		  standard conforming tar archives if they contain 8bit chars
		  in the filename. This is a common bug found in many other
		  implementations too.

		No additional problems on portability except with gnutar archives.
		But this is not a problem of BSD tar.


	2)	pax / ustar

		- Dumps core on every even/odd use.
		- Computes checksums only on the first 500 bytes of the 
		  tar header: not conforming to Posix 1003.1 standard.

		Note:	This claims to be a reference implementation for
			the Posix 1003.1 standard!


	3)	tar distributed with Solaris 2.3/2.4/2.5

		- Transfers more than 12 Bit from stat.st_mode (violating Posix)
		- Complains about "impossible file type" when reading 
		  tar archives which do not contain these illegal upper bits.

		- Does not handle non null terminated filenames correctly.
		  The standard allows filenames that are exactly 100 chars
		  and therefore are not null terminated. (Fixed in Solaris 2.5)

		For the obove reasons, Sun's tar is not conforming to Posix 1003.1.

		- Loops infinitely when trying to dump /dev/fd.
		  This makes it impossible to use Solaris tar on the root filesystem.


	4)	gnutar
		Claims not to be conforming to Posix 1003.1. (gnu is not tar)

		- Many bugs in implementation and design.
		  (e.g. when handling/creating multi volume archives)
		- The second logical EOF block in GNU-tar archives is missing
		  with a 50% chance.
		  This will cause correctly working tar implementations to complain
		  about an illegal/missing EOF in the tar archive.
		- Deeply nested directory trees will not be dumped:
		  Error message is: Too many open files
		  (This is a similar implementation bug as found in Solaris tar 
		   with the /dev/fd loop)
		- Hard links with long names to files with long names do not work.

		- GNU-tar cannot read Posix compliant tar archives with 
		  long file names if the filename prefix it at least 138 characters.
		  GNU-tar will think that it found an extended sparse GNU tar archive
		  and get out of sync for the rest of the archive.
		  See --sparse design bug description below.

		- GNU-tar even has a not yet identified bug which causes GNUtar
		  not to be able to partially read star archives if these archives
		  are not created with star -Hustar

		- Option --sparse produces archives which cannot be read by any 
		  other tar implementation known to me (except star), because
		  they will get "out of sync".
		  Posix 1003.1 conforming tar archives let gnutar get "out of sync"
		  even if the --portability option is used (see above).
		  This is a severe design bug in GNU-tar.

			Description:
			The size field in a tar archive cannot reflect the
			real size of a sparse file to have compatibility to 
			other implementations (this is also true for "star" archives).

			If the "sparse" file contains more than 4 holes,
			the "size" field in the GNU-tar control block does not
			reflect the total size of the (shrunk) sparse file in the archive
			because it does not count the 'sparse' extension headers.
			Posix conformant archives that use the name prefix field with more than
			137 characters will have a value != 0 on a field that
			that makes gnutar believe that such an extension
			header is present - GNU-tar will get out of sync.

			Note: The general rule for any tar is that it should
			be able to read any "tar" compliant data stream with
			the exception that enhancements to the standard
			only will fail on the files that contain the extension.
			Those files should be extracted as if they were 
			regular files.

		Note: I do not recommend GNU tar as an exchange format.
		      Use star -Hustar for maximum portability instead.

	5)	gnucpio

		- Splits long filenames at the leftmost '/' instead of the 
		  rightmost position of '/' required by my copy of the 
		  Posix standard.
		- The docs claim compatibility with gnutar.
		  But extraction of gnutar archives containing 'atime' gives 
		  funny filenames! (try this ...)
		- Octal numbers are left padded with ' ' instead of '0'.
		  The mode field contains more than the lower 12 bits from 
		  stat.st_mode.
		
