Writing HP cartridge tapes on a Sun 3

[Bob Niland]

re: "Does anybody know if it is possible to produce a tar tape on a Sun
     that is readable on an HP 300?  It seems that the HP uses some kind
     of strange format..."

from a Nov 1987 response to a similar question...

re: HP vs SUN format on 1/4-in. cartridge tapes

The sad news:  Sorry, you can't use 1/4-in.  cartridge tape to exchange data
	       with non-HP systems.  Why?  Read on...

As far as I know, there is no formal industry standard for 1/4-in.  tape
formats, like the ANSI standards for 1/2-in.  tape.  The variations between
vendors may include:  number of tracks, density, speed, direction, encoding,
etc.  The predominant HP standard is the 3M HCD-75 format, code-named
"Linus", as used on 88140LC/SC media (this is what you have).  A few vendors
have adopted QIC-02/24.  The HP 9142A drive uses "PCT" format,  also
incompatible with HCD.

The HCD-75 format was developed in the early 80's (well before QIC).  I have
no idea why it never became a standard outside HP.  It's rough
specifications are:  10,000 cpi, 16 track, MFM encoding.  The media is
pre-formatted by 3M into 1536-byte blocks (1024 data bytes plus 50%
redundancy for error recovery).  The 1.5Kb blocks are delimited by
full-track "keys", written by 3M.

The 3M designation for the 150-ft.  HP88140SC is DC615HC, and the 600-ft.
HP88140LC is DC600HC.  There is also a new HCD-134 format and "XTD" media,
suitable for 32-track drives.

The keys pre-formatting is critical.  It can be done only by 3M.  The
"certification" process done by our 'sdfinit' and 'mediainit' commands only
erases, verifies and spares the existing data frames.  It DOES NOT create
new keys or frames on a blank tape.  If you degauss an 88140 tape, or write
on it on a non-HCD-75 system, you destroy it's useability on HP systems.
This is why the reels are often labelled "DO NOT DEGAUSS".

SUN apparently uses QIC-24 format on QIC-02 drives.  I don't have complete
specs at hand, but what I could find says:  9 tracks, NRZI encoding and
variable length records.  SUN media appears to be 3M DC300XL.  The density
must be similar, since a 600-ft.  16-track HP tape holds 67 Mbytes, and a
600-ft.  9-track DC300XL holds 45 Mbytes.  In any case, I know from personal
experience that DC300XL media doesn't work in 88140-compatible HP drives.

Now, what can happen if you attempt interchange?

1. If the SUN system manages to write on your HP tape, the tape is ruined
   for further HP use.  You may be able to use it on the SUN after
   formatting it on the SUN (or whatever process they use to prep tapes, if
   any).

   Why would the SUN write on it?  Well, on HP tape drives, my understanding
   is that the drive will update the CS/80 logs on the tape (outside the
   region of data frames), regardless of whether or not the tape is
   write-protected (I doubt HP drives will write on a "foreign" tape).

   Unless you deliberately write on it, I don't really think a SUN will
   trash the tape.  QIC format does not allow selective re-writing of
   records like the HCD-75 format does.  There are probably also no "logs"
   because QIC format relies on read-while-write to prevent errors and has
   no other error recovery mechanism, and thus no use for logs.

2. The tape may be left rewound in a strange state.  Apart from the fact
   that SUN rewinds to the opposite end of the media from HP, the BOT/EOT
   conventions are different.

   The physical beginning and end of tape (BOT/EOT) on these cartridges is
   several holes punched in the tape, sensed optically through the little
   mirror opening in the cartridge.  The tape is NOT affixed to the takeup
   reels.  It is possible to rewind the tape off the hubs, so the drive
   firmware is "cautious".

   HP drives do not use the optical sense method; it was not sufficiently
   reliable.  We use the boundary keys to determine BOT/EOT, and always
   rewind the tape before unload/release.  If the tape is rewound to the
   BOT/EOT holes, it is outside the keys area, and the HP drive will
   probably time-out looking for keys, and thinks that the tape is spilled
   (or about to).  It will buzz and reject the cartridge to avoid damaging
   the tape by further attempts at tape motion.

   If you can see that the tape has not unspooled, you can try manual
   repositioning.  Wind the tape into the normal HP "rewound" state.  Watch
   carefully for the first BOT/EOT hole.  Park the hole toward the emptier
   reel (with respect to the mirror), plus an extra foot or so.  Be careful
   not to dump the tape.  It is very tricky to disassemble and reload one of
   these cartridges.

Regards,                                              Hewlett-Packard
Bob Niland        rjn at hpfcrjn.HP.COM                  3404 East Harmony Road
                  [hplabs|hpu...!hpfcse]!rjn          Ft Collins CO 80525-9599