A quick look,
and I think it's an stp (super TP) tape -- stp is from the
Harvard distribution. This would make sense, because that
was the standard back before tar.
As Ron pointed
out, tp (which Ken designed for DECTapes originally) puts the
index at the head of the tape (tar and later cpis threaded the
index inline). But it means its a fixed size and there were
some other issues (tp may have originally been in assembler
IIRC). On DECtape, tp worked pretty well/was pretty cool
because you could update a block, less so on 9-track which
when you re-wrote block N, you lost all blocks afterwards.
Also, I don't remember why now [probably the limits off the
directory], but it was typically in those days to take all the
files in a directory, turn them into a foo.a (ar format)
archive. So the stp image was a bunch of files:
dir1/mumble.a dir2/grumble.a dir3/bumble.a ...
You then needed
to unarchive the files within each directory. Also, remember
ar(1) when through some changes in format between 4-7th
editions as the compiler and linker matured. So watch out on
that front too...
Anyway, v6 tp
probably will read it, but if you poke around the TUHS and
bitkeeper archives for the original Harvard distribution,
stp.c should exist.