carry-tape flames

["Robert W. Kerns" <RWK@scrc-yukon.arpa>]

    Date: Thu, 8 Oct 87 13:49 EDT
    From: Chris Lindblad <CJL@REAGAN.AI.MIT.EDU>
    I second Gumby's suggestion, and go even further.  I'd love lispms to be able
    to read and write tar tapes.  Not a subset of the format.  Not a superset of
    the format.  Not something that's better.  Just tar tapes.  Doing the tar
    format exactly would be much better than improving on it, or inventing another
    format.
Not working on tape software myself, I'll leave the tar tarbaby
alone.  I will point out there is an ANSI standard tape format
that many systems support, as well.

Lest you all think I'm crazy, I will admit I think our tape situation
leaves a lot to be desired, but it seems kind of silly for ME to tell
YOU what I think is wrong with OUR tape software.

    I'm curious about another thing.  Happily, 9-track tapes are standardized
    that (at the level of just blocks bytes) they can be written on one
    manufacturer's machine and read on another's.  Is this true of those 3M
    cartridge tapes?  

Close.  There are a couple different formats, which are partly
interchangable.  3600's write one format, and later machines
write the other!  (And we're talking about at least three different
drives).  They're interchangable as long as you don't try to put
more than 20 Mb on a tape.  The 3600 format is a 5-track format.
The others use a 9-track format, writing 5 somewhat narrower
tracks where the 3600 format would put them, and then writing
4 more tracks between them.  Once it gets past the 5th track,
it's no longer compatible.   There are published standards for
both of these formats.

I believe we've seen a few cases of non-interchangability, but there's
always potential mis-alignment issues with tape of any type, and
we have a large sample to deal with, given the thousands of tapes
we send out.