Multiple cpio/tar files on Apple Tape

[tony cooper]

In article <1990Mar26.062901.8016 at noao.edu> tody at noao.edu (Doug Tody X217) writes:
>> Hello,
>> Has anyone out there used the Apple Tape Cartridge to store
>> multiple tar/cpio file archives? It is clear that the "norewind"
>> device must be used, but does the tape driver write and eof mark?
>
>Yes.  All unix tape drivers automatically write an EOT (double tape mark)
>when a file opened for writing is subsequently closed.  If closed no-rewind,
>the tape is left positioned between the file marks and the next file will
>overwrite the second tape mark, giving you an EOF between the files (those

I don't know if Tody is using logic to say that the Apple tc tape driver
write EOT's. But the premise is wrong. It is not true that all unix tape
drivers behave as described. To write two tape marks and to position the 
tape between filemarks requires that the tape drive can backspace. The
Apple tape drive can backspace and uses this method for EOT's. But not all
drives can backspace. The TEAC drives cannot and so they use a different
mechanism to recognize the end of tape.

Tony Cooper
tony at popserver.stanford.edu