What is the deal with these HP tape drives?

The HP tapes for the 9144 and 9145 have a special HP format, you have to buy them pre-formatted. The drive itself is supposedly incapable of performing the formatting task. Perhaps someone else on the list has the actual format info - my book seems to have disappeared, again!! But the 9144 is a 16 track and the 9145 is 32 track. The 9145 *will* read a tape from a 9144 but not vice versa.

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.