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On Mon, 16 Sep 1996 19:38:18 EST  Fletcher Christian wrote:

> About the HP tapes. Does anyone know what the story is?? Are the mechanisms
> the same as standard QIC02 1/4" drives (ie are they only formated diferently) or  
> are ther actual hardware differences?

Hardware differences.  For those interested (and the archives ;-) an
explanation is below of the differences between the HP drives and QIC.

Regards,

Giles


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From: blh@hpuerca.atl.hp.com (Bill Hassell)
Newsgroups: comp.sys.hp.hardware
Subject: Re: HP9144 tape unit - What is the capacity?
Date: 30 Jan 1996 16:46:22 GMT
Organization: the HP Response Center, Atlanta
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Fred Aker (af470@FreeNet.Carleton.CA) wrote:

: I have on my HP9000/360 but have no information on it at all.
: Can anyone give me a little more info on this guy?

  9144 can store 16 megs or 67 megs on the two special format tapes.
  It requires HP-formatted tapes that look like QIC tapes, but the
  format preceded QIC.  Here's a note from Bob Niland on the subject:


==========================================================================

There are a number of formats employing seemingly identical 1/4-inch
cartridges.  The most common are the various QIC definitions (QIC = Quarter
Inch Committee).  Sun and Apollo systems, for example, often use QIC-24 (60
Mb).  Traditional HP drives do not use the QIC format, but rather one
invented by 3M some five years before QIC.  It is called HCD format.

Inserting an HP cartridge in a QIC drive leads at the very least to
frustration, and potentially to permanent damage to the HP tape.

                 --------------------------------------
    		       The one-minute summary

Attempting to use a QIC tape in an HP HCD drive results in:

  1. Tape rejected.
  2. Possible tape unspool after repeated attempts.

Attempting to use an HCD tape in a QIC drive results in:

  1. No data exchanged.
  2. An apparently damaged tape (rewind scenario).
  3. A probably destroyed tape if a manual (reposition spill scenario).
  4. A definitely destroyed tape (write scenario).

                 --------------------------------------

Cartridge Tape Specification Overview:

 .====================.=========================.==========================.
 | Characteristic     | HCD Cartridge Tape      | QIC Cartridge Tape       |
 |====================|=========================|==========================|
 | Approx. Incep. date| 1980                    | 1985                     |
 |--------------------|-------------------------|--------------------------|
 | Mechanical form    | 3M DC600                | 3M DC600                 |
 |   factor           |                         |                          |
 | Merchandising name | <none, really>          | QIC-24 or QIC-120        |
 |--------------------|-------------------------|--------------------------|
 | Typical supplier   | HP (for HP customers)   | any discounter           |
 |--------------------|-------------------------|--------------------------|
 | Generic designation| DC600HC, DC615HC,       | DC600A, DC615A           |
 |                    |   DC600XTD, DC615XTD    |                          |
 |--------------------|-------------------------|--------------------------|
 | Tape pre-format    | Full-track 3M HCD-75    | <none>                   |
 |                    |   or modified HCD-134   |                          |
 | Data format        | MFM                     | NRZI                     |
 |--------------------|-------------------------|--------------------------|
 | EOT/BOT            | Delimited by pre-format | Optical tape sense holes |
 | Rewind position    | Right spool empty.      | Left spool empty.        |
 |--------------------|-------------------------|--------------------------|
 | Capacity           | 67 or 134 Mbytes        | 60 or 120 Mbytes         |
 | Number of tracks   | 16 or 32                | 9 or 15                  |
 |--------------------|-------------------------|--------------------------|
 | Access types       | Random (re-writeable)   | Serial only              |
 |                    |   or serial             |                          |
 | Average seek (60M) | 2 minutes               | 20 minutes               |
 |--------------------|-------------------------|--------------------------|
 | Error control      | Read-while-write        | Read-while-write only    |
 |                    |   plus ECC              |                          |
 `========================================================================='

As you can see, HCD has some advantages.  Errors missed by read-after-write
may still be corrected by ECC when read later.  Tapes may be "certified" and
re-certified by end users, sparing bad blocks.  The random-access capability
allows software to treat the tape like a *very* slow disk drive.  Disk-image
cartridge tape backups are mountable as read/write volumes, and may be
safely written upon.  Random access is faster, because the location of every
record can be calculated, due to the pre-formatting.  An exhaustive search
is not required.  This decade-old format has given us satisfactory service.
But, enough drifting away from the topic...


HCD and QIC cartridges are mechanically identical.  An HCD cartridge will
fit in a QIC drive, and vice-versa.

So what is the problem?

 * HCD tapes are preformatted by 3M or a 3M licensee.  A full-track factory
   write head lays down fixed physical records on the tape.  No HCD drive
   ever writes on these record headers (called "keys"); only in between
   them.  HP "format" and/or "mediainit" user processes merely "certify",
   performing read/write tests, sparing bad blocks and updating logs.

   The read/write heads in the drives are either 1/16- or 1/32-track.  Keys,
   being full-track, cannot be re-written in the field.

 * The keys also do not extend to the physical BOT/EOT sense holes in the
   tape.  When the first HP drives were developed in the early 80s, optical
   sensing was deemed too unreliable, so all HP drives use boundary keys to
   denote BOT/EOT.  (QIC tapes are more like traditional 1/2-inch 9-track
   media.  The tapes have no pre-formatting, so QIC drives must rely on the
   sense holes for BOT/EOT.)

 * If you put a QIC tape (blank or written) in an HP HCD drive, the HP drive
   will search "uptape" (wrong way past EOT on QIC) for the nearest key,
   fail to find one, time-out, buzz, release (unload) the tape and
   illuminate the FAULT indicator.  No data lost, but no data is read or
   written either.  Repeated attempts risk a tape spill.

 * If the you put an HCD tape in a QIC drive, the drive will "rewind" it (to
   the wrong end of the tape by HP conventions) and OUTSIDE the keys region.

   Suppose the tape is removed from the QIC drive and re-inserted in an HP
   drive.  The HP drive, as in the preceding example, will search "uptape"
   for a key (again, in the wrong direction due to the QIC rewind), not find
   a key in a reasonable time, and reject the tape for fear of spilling tape
   if the search continues.  It will buzz, release and FAULT.  Repeated
   attempts risk a tape spill.

   The tape may be MANUALLY wound, in the COUNTER-INTUITIVE direction, to
   reposition it inside the keys.  If re-inserted in the HP drive, it will
   properly load (after adding an extra minute to the load time because it
   was rewound to the wrong end).

   I say "counter-intuitive" because tape motion inside the cartridge is in
   the OPPOSITE direction from drive wheel motion, and the tensioning band
   makes it difficult to assess which way the tape is supposed to spool.
   Now, also please note that in the construction of DC600 media, the tape
   ends are not affixed to the reels...

 * Given a mis-positioned cartridge, should someone manually wind in the
   intuitive {i.e. incorrect} direction, or risk repeated access attempts,
   the tape unspools.  Disassembly and re-spooling of DC600 tapes is a
   nightmare for the inexperienced.  In a past life I re-loaded several
   DC100A cartridge tapes.  Not fun.  The probability of reloading the tape
   without damage is low.

 * If, on the other hand, the HCD tape was left in the QIC drive, two more
   scenarios obtain.  The QIC drive has no clue that this is an HCD tape.

   1. The HCD data structures just look like noise.  Any attempt to read
      an HCD tape simply fails or returns garbage data.  If the tape is
      removed after a read attempt, the rewind scenario above prevails.

   2. A QIC drive will happily WRITE on an HCD tape.  This destroys both
      existing data AND the HCD preformatting keys.  If the preformatting is
      ever lost, the tape can NEVER be used in an HCD drive again.  (This
      problem can also happen subsequent to degaussing an HCD tape.)

      What happens back at the HP drive?  Apart from the rewind/time-out
      problem, as soon as the HP drive detects a trashed key, it will FAULT
      and reject the tape.  Only 3M can (re)format an HCD tape, and I doubt
      that they offer such a service.

--
              
           __?__
          /     \
         / ^   ^ \
        ( (o) (o) )
         \       /
*=oOOO======(_)=====OOOo====*=====================================*
|   Bill Hassell            |  Hewlett-Packard Response Center    |
|   System Administrator    |  blh@atl.hp.com  /  Atlanta, GA.    |
*=============Oooo.=========*=====================================*
      .oooO   (   )
       (   )    ) /   "There are two types of computer users in the
        \ (    (_/     world...those that have lost data, and those
         \_)           that are going to."        (blh, circa 1972)


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